chore: refactor pull request template for better structure and guidance

[guilhermercarvalho]

Fixes #5534

Summary

This pull request updates the pull request template to improve structure and provide clearer guidance for contributors. The changes include:

• Clearly separate UI (frontend) and API (backend) sections
• Add a before/after screenshot table for UI changes
• Include checklists for tasks, testing, documentation, accessibility, etc.
• Preserve Codespaces testing instructions in a collapsible block
• Add visual hints (ASCII art comments) to guide removal of irrelevant sections
• Update API documentation instruction to use composer openapi
• Add optional items: browser testing, accessibility, design review, capabilities
• Include AI disclosure checkbox for transparency

These improvements address the feedback from the previous attempt (#6200) and align the template with current project needs.

New Pull Request Template

Below is the new template file content:

Resolves: # <!-- related github issue -->

## 📝 Summary

A concise description of what this PR does and why.

## 🧪 How to test
<!--
IMPORTANT: The "How to see this running using GitHub Codespaces" details block SHOULD NOT be included in the final template.
Testing instructions should be written specifically for each PR,
describing the steps needed to validate the proposed changes.

Example:
1. Access the signatures page
2. Upload a test PDF
3. Click "Sign" and verify the modal opens correctly
4. Confirm the signature was applied

Feel free to paste terminal commands or URLs that help reviewers follow along.
-->

<details>
<summary>How to see this running using GitHub Codespaces</summary>

### 1. Open the Codespace
- Authenticate to GitHub
- Go to the branch: [chore/reduce-configure-check-time](https://github.com/LibreSign/libresign/tree/chore/reduce-configure-check-time)
- Click the `Code` button and select the `Codespaces` tab.
- Click **"Create codespace on feat/customize-signature-stamp"**

### 2. Wait for the environment to start
- A progress bar will appear on the left.
- After that, the terminal will show the build process.
- Wait until you see the message:
  ```bash
  ✍️ LibreSign is up!
  ```
  This may take a few minutes.

### 3. Access LibreSign in the browser
- Open the **Ports** tab (next to the **Terminal**).
- Look for the service running on port **80**.
- Hover over the URL and click the **globe icon** 🌐 to open it in your browser.

### 4. (Optional) Make the service public
- If you want to share the app with people **not logged in to GitHub**, you must change the port visibility:
  - Click the three dots `⋮` on the row for port 80.
  - Select `Change visibility` → `Public`.

### 5. Login credentials
- **Username**: `admin`
- **Password**: `admin`

Done! 🎉
You're now ready to test this.
</details>

## 🎨 UI / Front‑end changes

<!--
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▒▒███  ▒▒███ ▒▒███
 ▒███   ▒███  ▒███
 ▒███   ▒███  ▒███
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 ▒███   ▒███  ▒███
 ▒▒████████   █████
  ▒▒▒▒▒▒▒▒   ▒▒▒▒▒

Feel free to remove this section when your PR only affects the backend/API code.
-->

- [ ] ... <!-- Describe the tasks performed here (e.g., layout adjustment, new feature X) -->
- [ ] Screenshots before/after (add images or links)

### 🚧 Tasks
<!-- Add here the list of tasks that is necessary to do before merge this PR. As example: update the package X, merge the PR y. If isn't necessary, fell free to remove this block -->
- [ ] ...

🏚️ Before | 🏡 After
--- | ---
<!-- Add screenshot  |  Add screenshot -->

<!-- ☀️ Light theme | 🌑 Dark theme → Please test and document both themes -->

- [ ] Tested in multiple browsers (Chrome, Firefox, Safari) – *optional but appreciated*
- [ ] Components, Unit (with vitest) and/or e2e (with Playwright) tests added - *Required*
- [ ] Accessibility verified (contrast, keyboard navigation, screen reader friendly) – *if applicable*
- [ ] Design review approved – *optional, link to feedback if available*
- [ ] Documentation updated (if applicable) – [docs repository](https://github.com/LibreSign/documentation/)

## ⚙️ API / Back‑end changes

<!--
   █████████   ███████████  █████
  ███▒▒▒▒▒███ ▒▒███▒▒▒▒▒███▒▒███
 ▒███    ▒███  ▒███    ▒███ ▒███
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 ▒███▒▒▒▒▒███  ▒███▒▒▒▒▒▒   ▒███
 ▒███    ▒███  ▒███         ▒███
 █████   █████ █████        █████
▒▒▒▒▒   ▒▒▒▒▒ ▒▒▒▒▒        ▒▒▒▒▒

Feel free to remove this section when your PR only affects the frontend/UI code.
-->

- [ ] ... <!-- Describe the API/service/architecture changes here -->
- [ ] Unit and/or integration tests added – *required for backend changes*
- [ ] Capabilities updated (if applicable) – if adding/modifying Nextcloud capabilities
- [ ] Documentation updated (if applicable) - [docs repository](https://github.com/LibreSign/documentation)
- [ ] API documentation updated with the command `composer openapi` if necessary <!-- This generates the openapi.json file -->

### 🚧 Tasks
<!-- Add here the list of tasks that is necessary to do before merge this PR. As example: update the package X, merge the PR y. If isn't necessary, fell free to remove this block -->
- [ ] ...

## ✅ Checklist

- [ ] I have read and followed the [contribution guide](CONTRIBUTING.md).
- [ ] ... (list your own tasks here)

## 🤖 AI (if applicable)

- [ ] The content of this PR was partially or fully generated using AI

Example of Filled-out Template

Here is an example of how the template would be filled out for a hypothetical UI change (e.g., adjusting button styles):

Resolves: #1234

##  📝 Summary

Adjust button padding to match Nextcloud design guidelines.

##  🧪 How to test

1. Open the settings page in LibreSign.
2. Locate the "Save" button in the general settings section.
3. Inspect the button's padding using browser devtools; it should now be `12px 16px` (previously `8px 12px`).
4. Verify that the button appearance remains consistent in both light and dark themes.

## 🎨 UI / Front‑end changes

- [x] Adjusted button padding in CSS (`.button` class)
- [x] Screenshots before/after

🏚️ Before | 🏡 After
--- | ---
![before](https://placehold.co/300x200?text=Before) | ![after](https://placehold.co/300x200?text=After)

<!-- ☀️ Light theme | 🌑 Dark theme → Please test and document both themes -->

- [X] Tested in multiple browsers (Chrome, Firefox, Safari)  – *optional but appreciated*
- [X] Components, Unit (with vitest) and/or e2e (with Playwright) tests added - *Required*
- [ ] Accessibility verified (contrast, keyboard navigation, screen reader friendly) – *not applicable*
- [ ] Documentation updated - *not applicable*

## ✅ Checklist

- [x] I have read and followed the [contribution guide](CONTRIBUTING.md).
- [ ] ... (no additional tasks)

## 🤖 AI (if applicable)

- [ ] The content of this PR was partially or fully generated using AI

[welcome]

Thanks for opening your first pull request in this repository! ✌️

[vitormattos]

Nice! Thanks a lot!

Follow some suggestions.

[guilhermercarvalho]

I included a comment clarifying that the Codespaces block is a permanent part of the template, but that specific testing instructions must be written manually for each PR. This addresses the requirement from issue #5534 to retain the Codespaces instructions while also guiding contributors on how to use the template correctly.

[vitormattos]

/backport to stable33

[vitormattos]

/backport to stable32

[vitormattos]

Thanks by your dedicated time 💚