feat: add miniPaint stack (paint.pivoine.art)

Added new paint service stack to the docker-compose infrastructure:

- **Paint stack** (paint.pivoine.art):
  - miniPaint: Web-based image editor built from GitHub
  - Multi-stage Docker build clones from https://github.com/viliusle/miniPaint
  - Features: layers, filters, drawing tools, text, shapes support
  - Client-side processing with no server uploads
  - Stateless architecture (no backups needed)

Infrastructure updates:
- Created paint/compose.yaml with Traefik routing and SSL
- Created paint/Dockerfile with Node.js build stage and nginx serve
- Added PAINT environment variables to arty.yml
- Updated compose.yaml include list
- Updated CLAUDE.md documentation

All services integrated with Traefik for SSL termination and include
Watchtower auto-update labels.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CLAUDE.md

@@ -23,6 +23,7 @@ Root `compose.yaml` uses Docker Compose's `include` directive to orchestrate mul
 - **vault**: Vaultwarden password manager (SQLite)
 - **joplin**: Joplin Server note-taking and sync platform (PostgreSQL)
 - **vert**: VERT file format converter (WebAssembly-based, stateless)
+- **paint**: miniPaint web-based image editor (built from GitHub)
 - **restic**: Backrest backup system with restic backend
 - **sablier**: Dynamic scaling plugin for Traefik
 - **vpn**: WireGuard VPN (wg-easy)
@@ -272,6 +273,27 @@ Simply access https://vert.pivoine.art and drag/drop files to convert between fo
 
 **Note**: VERT is stateless and doesn't require backups as no data is persisted.
 
+### Paint (paint/compose.yaml)
+miniPaint web-based image editor built from GitHub:
+- **paint**: miniPaint app exposed at `paint.pivoine.art:80`
+  - Online image editor with layer support
+  - Built directly from https://github.com/viliusle/miniPaint
+  - Supports PNG, JPG, GIF, WebP formats
+  - Features: layers, filters, drawing tools, text, shapes
+  - Client-side processing (no uploads to server)
+  - No persistent data storage required
+  - Stateless architecture
+
+**Build Process**:
+- Multi-stage Docker build clones from GitHub
+- Builds using Node.js 18
+- Serves static files via nginx
+
+**Usage**:
+Access https://paint.pivoine.art to use the image editor. All editing happens in the browser - images are not uploaded to the server.
+
+**Note**: miniPaint is stateless and doesn't require backups as no data is persisted.
+
 ### Restic (restic/compose.yaml)
 Backrest backup system with restic backend:
 - **backrest**: Backrest web UI exposed at `restic.pivoine.art:9898`