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/backend/.env.example

@@ -0,0 +1,21 @@
+# Database
+DATABASE_URL=sqlite:///./data/ai_photo_edit.db
+
+# Security
+SECRET_KEY=your-secret-key-here-change-in-production
+ALGORITHM=HS256
+ACCESS_TOKEN_EXPIRE_MINUTES=30
+
+# AI Provider (configure based on your provider)
+AI_PROVIDER=openai
+OPENAI_API_KEY=your-openai-api-key-here
+# Alternative providers (uncomment as needed)
+# AI_PROVIDER=stability
+# STABILITY_API_KEY=your-stability-api-key-here
+
+# File Storage
+DATA_DIR=/app/data
+MAX_UPLOAD_SIZE_MB=50
+
+# CORS
+CORS_ORIGINS=http://localhost:3000,http://localhost:5173