fix(icons): apply fill to AddCircleIcon path, drop full-canvas rect

[alexquincy]

Summary

AddCircleIcon's SVG put fill={fill} (currentColor by default) on a full-canvas 48×48 rect and left the actual icon path unfilled. As a result the icon rendered as a solid rectangle of text color with a black plus-in-circle outline on top (SVG default-fill behavior), rather than a clean outlined-plus-in-circle glyph.

This drops the background rect and applies fill={fill} to the icon path, so AddCircleIcon renders like the @mui/icons-material/AddCircleOutline it's meant to replace in consumers.

Before / after SVG

<!-- before -->
<svg viewBox="0 0 48 48">
  <path d="M0 0h48v48h-48z" fill={fill} />   <!-- background rect -->
  <path d="M26 14h-4v8..." />                 <!-- icon, unfilled -->
</svg>

<!-- after -->
<svg viewBox="0 0 48 48">
  <path d="M26 14h-4v8..." fill={fill} />     <!-- icon, currentColor -->
</svg>

The icon d attribute is unchanged; only the paint instructions moved.

Context

This is exposed by meshery/meshery#18796, which swaps @mui/icons-material/AddCircleOutline → AddCircleIcon from @sistent/sistent. Without this fix, that swap produces a visible regression (solid-colored rectangle with black outline instead of a clean outline). AddCircleIcon wasn't used anywhere in meshery/ui before #18796, which is why this bug went unnoticed.

Test plan

• npm test — 7 suites, 21 tests all pass.
• Visual spot-check: <AddCircleIcon /> renders matching @mui/icons-material/AddCircleOutline on both light and dark themes.

[gemini-code-assist]

Code Review

This pull request simplifies the AddCircleIcon SVG by removing an unnecessary background path and applying the fill property directly to the icon path. A review comment suggests renaming the component AddIconCircleBordered to match the filename AddCircleIcon.tsx for better consistency and maintainability.