feat: add README and figure generation script for padding constructor

lib/node_modules/@stdlib/plot/vega/padding/ctor/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2026 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# Padding
+
+> [Padding][@stdlib/plot/vega/padding] constructor.
+
+<section class="intro">
+
+The [padding][@stdlib/plot/vega/padding] directive defines the spacing (in pixels) around the main chart group area. It determines the gap between the boundaries of the root visualization area and the inner rendering layout.
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var Padding = require( '@stdlib/plot/vega/padding/ctor' );
+```
+
+#### Padding( \[options] )
+
+Returns a `Padding` instance.
+
+```javascript
+var padding = new Padding();
+// returns <Padding>
+
+padding = new Padding({
+    'left': 80,
+    'right': 80,
+    'top': 80,
+    'bottom': 80
+});
+// returns <Padding>
+```
+
+<!-- <figure class="figure" align="center" label="fig:padding" src="./docs/img/figure_padding.svg" alt="A visualization showing padding margins around the main chart area."> -->
+
+<div class="figure" align="center" data-figure="fig:padding">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding.svg" alt="A visualization showing padding margins around the main chart area.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+The `options` object has the following properties:
+
+-   **bottom**: bottom padding (in pixels). Default: `0`.
+-   **left**: left padding (in pixels). Default: `0`.
+-   **right**: right padding (in pixels). Default: `0`.
+-   **top**: top padding (in pixels). Default: `0`.
+
+* * *
+
+### Methods
+
+<a name="method-to-json"></a>
+
+#### Padding.prototype.toJSON()
+
+Serializes an instance to a JSON representation.
+
+```javascript
+var padding = new Padding({
+    'left': 80,
+    'right': 80,
+    'top': 80,
+    'bottom': 80
+});
+
+var json = padding.toJSON();
+// returns { 'left': 80, 'right': 80, 'top': 80, 'bottom': 80 }
+```
+
+This method is implicitly invoked by `JSON.stringify`.
+
+* * *
+
+### Writable Properties
+
+<a name="prop-top"></a>
+
+#### Padding.prototype.top
+
+Top padding (in pixels).
+
+```javascript
+var padding = new Padding({
+    'left': 80,
+    'right': 80,
+    'top': 0,
+    'bottom': 80
+});
+
+var v = padding.top;
+// returns 0
+
+padding.top = 100;
+
+v = padding.top;
+// returns 100
+```
+
+<!-- <figure class="figure" align="center" label="fig:padding_top_0" src="./docs/img/figure_padding_top_0.svg" alt="Padding with top set to 0."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_top_0">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_top_0.svg" alt="Padding with top set to 0.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+<!-- <figure class="figure" align="center" label="fig:padding_top_100" src="./docs/img/figure_padding_top_100.svg" alt="Padding with top set to 100."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_top_100">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_top_100.svg" alt="Padding with top set to 100.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+<a name="prop-bottom"></a>
+
+#### Padding.prototype.bottom
+
+Bottom padding (in pixels).
+
+```javascript
+var padding = new Padding({
+    'left': 80,
+    'right': 80,
+    'top': 80,
+    'bottom': 0
+});
+
+var v = padding.bottom;
+// returns 0
+
+padding.bottom = 100;
+
+v = padding.bottom;
+// returns 100
+```
+
+<!-- <figure class="figure" align="center" label="fig:padding_bottom_0" src="./docs/img/figure_padding_bottom_0.svg" alt="Padding with bottom set to 0."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_bottom_0">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_bottom_0.svg" alt="Padding with bottom set to 0.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+<!-- <figure class="figure" align="center" label="fig:padding_bottom_100" src="./docs/img/figure_padding_bottom_100.svg" alt="Padding with bottom set to 100."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_bottom_100">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_bottom_100.svg" alt="Padding with bottom set to 100.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+<a name="prop-left"></a>
+
+#### Padding.prototype.left
+
+Left padding (in pixels).
+
+```javascript
+var padding = new Padding({
+    'left': 0,
+    'right': 80,
+    'top': 80,
+    'bottom': 80
+});
+
+var v = padding.left;
+// returns 0
+
+padding.left = 130;
+
+v = padding.left;
+// returns 130
+```
+
+<!-- <figure class="figure" align="center" label="fig:padding_left_0" src="./docs/img/figure_padding_left_0.svg" alt="Padding with left set to 0."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_left_0">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_left_0.svg" alt="Padding with left set to 0.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+<!-- <figure class="figure" align="center" label="fig:padding_left_130" src="./docs/img/figure_padding_left_130.svg" alt="Padding with left set to 130."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_left_130">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_left_130.svg" alt="Padding with left set to 130.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+<a name="prop-right"></a>
+
+#### Padding.prototype.right
+
+Right padding (in pixels).
+
+```javascript
+var padding = new Padding({
+    'left': 80,
+    'right': 0,
+    'top': 80,
+    'bottom': 80
+});
+
+var v = padding.right;
+// returns 0
+
+padding.right = 130;
+
+v = padding.right;
+// returns 130
+```
+
+<!-- <figure class="figure" align="center" label="fig:padding_right_0" src="./docs/img/figure_padding_right_0.svg" alt="Padding with right set to 0."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_right_0">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_right_0.svg" alt="Padding with right set to 0.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+<!-- <figure class="figure" align="center" label="fig:padding_right_130" src="./docs/img/figure_padding_right_130.svg" alt="Padding with right set to 130."> -->
+
+<div class="figure" align="center" data-figure="fig:padding_right_130">
+    <img src="https://cdn.jsdelivr.net/gh/gururaj1512/stdlib@eb64ecc323cbaabf1a0191aea50fcb6ab65e750e/lib/node_modules/@stdlib/plot/vega/padding/ctor/docs/img/figure_padding_right_130.svg" alt="Padding with right set to 130.">
+    <br>
+</div>
+
+<!-- </figure> -->
+
+* * *
+
+### Read-Only Properties
+
+<a name="prop-properties"></a>
+
+#### Padding.prototype.properties
+
+An array of Padding property names.
+
+```javascript
+var padding = new Padding();
+
+var props = padding.properties;
+// returns [ 'bottom', 'left', 'right', 'top' ]
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="examples">
+
+## Examples
+
+```javascript
+var Padding = require( '@stdlib/plot/vega/padding/ctor' );
+
+var padding = new Padding();
+console.log( padding.toJSON() );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<section class="references">
+
+</section>
+
+<!-- /.references -->
+
+<section class="related">
+
+## See Also
+
+-   <span class="package-name">[`@stdlib/plot/vega/builder`][@stdlib/plot/vega/builder]</span><span class="delimiter">: </span><span class="description">Vega visualization builder.</span>
+
+</section>
+
+<!-- /.related -->
+
+<section class="links">
+
+[@stdlib/plot/vega/builder]: https://github.com/stdlib-js/stdlib/tree/refactor/plot/lib/node_modules/%40stdlib/plot/vega/builder
+
+[@stdlib/plot/vega/padding]: https://github.com/stdlib-js/stdlib/tree/refactor/plot/lib/node_modules/%40stdlib/plot/vega/padding/ctor
+
+<!-- <related-links> -->
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->