paintplus: vendor the app source and rename from EditmaskwithAI

Bring the full EditmaskwithAI application into the repo under paintplus/
(429 files) so the service is self-contained — the installer copies the
vendored source to ~/docker/paintplus/src instead of cloning at runtime.

Rename to PaintPlus (service + branding; app logic untouched):
- services/editmaskwithai.sh -> services/paintplus.sh (register_service
  paintplus, install_paintplus, ~/docker/paintplus, Caddy paintplus:8000,
  Authelia option preserved)
- container names -> paintplus across docker-compose*.yml; dev network
  -> paintplus-network
- browser <title> -> "PaintPlus - AI Image Editor"; README heading ->
  PaintPlus with upstream provenance note
- README utilities table: editmaskwithai -> paintplus

Backend/frontend code (help strings referencing the old container name,
the ai_photo_edit.db filename) is intentionally left as-is to avoid
touching application logic.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nb2vJ8W7bHKx1JXVvpCraH

paintplus/CONTRIBUTING.md

@@ -0,0 +1,86 @@
+# Contributing to AI Photo Edit
+
+Thank you for your interest in contributing to AI Photo Edit!
+
+## Development Setup
+
+1. Fork the repository
+2. Clone your fork
+3. Create a feature branch
+4. Make your changes
+5. Test your changes
+6. Submit a pull request
+
+## Development Environment
+
+### Using Docker (Recommended)
+
+```bash
+# Start dev environment with hot-reload
+docker-compose -f docker-compose.dev.yml up
+```
+
+### Local Development
+
+**Backend**
+```bash
+cd backend
+python -m venv venv
+source venv/bin/activate  # On Windows: venv\Scripts\activate
+pip install -r requirements.txt
+uvicorn app.main:app --reload
+```
+
+**Frontend**
+```bash
+cd frontend
+npm install
+npm run dev
+```
+
+## Code Style
+
+### Python (Backend)
+- Follow PEP 8
+- Use type hints where appropriate
+- Add docstrings to functions and classes
+
+### JavaScript/React (Frontend)
+- Use functional components with hooks
+- Follow React best practices
+- Use meaningful variable names
+
+## Pull Request Process
+
+1. Update the README.md with details of changes if needed
+2. Ensure all tests pass
+3. Update documentation as needed
+4. Get approval from maintainers
+5. Squash commits if requested
+
+## Reporting Bugs
+
+When reporting bugs, please include:
+- Description of the issue
+- Steps to reproduce
+- Expected behavior
+- Actual behavior
+- Screenshots if applicable
+- Environment details (OS, Docker version, etc.)
+
+## Feature Requests
+
+We welcome feature requests! Please:
+- Check if the feature already exists
+- Explain the use case
+- Describe the expected behavior
+- Consider if it aligns with project goals
+
+## Code of Conduct
+
+- Be respectful and inclusive
+- Welcome newcomers
+- Focus on constructive feedback
+- Respect differing opinions
+
+Thank you for contributing!