Add comprehensive CONTRIBUTING.md with gamepad mapping guidelines

[Copilot]

Describe your changes

Expanded CONTRIBUTING.md from basic guidelines to a comprehensive, concise contribution guide. Primary focus: lowering barriers for community gamepad mapping contributions.

New sections:

• Gamepad Mapping Guide (7-step process): VID/PID extraction, button/axis mapping with links to online gamepad testers, schema selection (Hedgehog/Plumber/Xross), code examples for standard and custom mappings
• Development Workflow: Streamlined setup verification and typical workflow
• Testing Protocols: Checklists for gamepad mappings (10 items) and code changes (6 items)
• Code Style: JSDoc requirements with examples, ESLint/EditorConfig rules
• PR Process: Submission workflow, commit guidelines, pre-submission checklist
• Architectural Principles: Design boundaries (zero runtime dependencies, no build transforms, browser-only)

Key additions:

// VID/PID extraction example
const gamepad = navigator.getGamepads()[0]
console.log('ID:', gamepad.id)
// "057e-2009-Nintendo Switch Pro Controller"
//  ^^^^ ^^^^ Name
//  VID  PID

Schema comparison table for button layout selection, custom mapping examples for non-standard controllers, icon directory reference with requirement that icons must be human-created and never AI-generated.

Streamlined content:

• Simplified fork/clone instructions (developers know how to use GitHub)
• Removed verbose command reference table (commands are self-evident)
• Replaced inline HTML test tool with links to existing online gamepad testers (Gamepad Tester, HTML5 Gamepad Tester)
• Clarified prerequisites: "One or more gamepads" required for development

Describe your testing

N/A - documentation only. Verified markdown structure and section completeness against issue requirements.

Issue ticket number and link

#[handled by system]

Checklist before requesting a review

• I have performed a self-review of my code
• The code passes lint checks.
• The code has been tested for regressions of existing features.
• I have considered adding unit tests for any new code.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add CONTRIBUTING.md for mapping & testing guidelines</issue_title>
<issue_description>## Feature Request
Add a CONTRIBUTING.md to document the process for adding new gamepad mappings, test protocols, and general contribution expectations.

Why This Matters

The gamepad model database is complex and requires specific information. A contribution guide would:

• Help community members add new controller mappings
• Standardize the testing process
• Reduce back-and-forth in PRs
• Grow the controller database faster

Proposed Sections

1. Adding a New Gamepad Mapping

## Adding a New Gamepad Mapping

### Information Needed
1. **Vendor ID & Product ID**: Found in browser console
   ```javascript
   const gamepad = navigator.getGamepads()[0]
   console.log(gamepad.id)
   // Example: "057e-2009-Nintendo Switch Pro Controller"
   //          VID  PID   Name

2. Button Mapping: Test each button and record index
3. Axis Mapping: Test each stick/trigger and record axis + direction
4. Schema: Which button layout? (Nintendo/Xbox/PlayStation)
5. Icon: Which icon represents this gamepad?

Testing Your Mapping

1. Create a test HTML file
2. Connect your gamepad
3. Test all buttons and axes
4. Verify with multiple browsers if possible

#### 2. Code Style Guidelines
```markdown
## Code Style

- Use JSDoc for all public APIs
- Follow existing naming conventions
- Run `npm run lint` before committing
- Add tests for new features
- Keep PRs focused on single changes

3. Testing Protocol

## Testing Protocol

### For Gamepad Mappings
- [ ] Test all face buttons
- [ ] Test D-pad in all directions
- [ ] Test both analog sticks (including click)
- [ ] Test shoulder buttons
- [ ] Test triggers (analog if applicable)
- [ ] Test center buttons (start/select)
- [ ] Test rumble/vibration if supported

### For Code Changes
- [ ] Add unit tests
- [ ] Run full test suite: `npm test`
- [ ] Test in Chrome and Firefox
- [ ] Update JSDoc if API changed

4. Pull Request Template

## Pull Request Checklist

- [ ] Tests pass locally
- [ ] JSDoc updated (if applicable)
- [ ] CHANGELOG.md updated
- [ ] Follows code style guidelines
- [ ] For gamepad mappings: tested on real hardware

Implementation

Create CONTRIBUTING.md in repository root with:

• Getting started (fork, clone, install)
• Development workflow
• Gamepad mapping contribution guide
• Code style and conventions
• Testing requirements
• PR process
• Code of conduct reference

This would significantly lower the barrier for community contributions, especially for adding new gamepad models.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add CONTRIBUTING.md for mapping & testing guidelines #71

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