Implement complete AI Photo Edit tool with mask-scoped regeneration

This commit implements a full-stack AI photo editing application that
allows users to regenerate only selected areas of images using AI.

Features implemented:
- Frontend (React + Fabric.js):
  * Interactive canvas with selection tools (rectangle, ellipse, lasso)
  * Real-time selection preview and editing
  * Mode toggle (A: patch only, B: patch + context)
  * Feather slider for edge blending (0-50px)
  * Prompt input for AI instructions
  * Edit history viewer with revert capability
  * Responsive UI with dark theme

- Backend (FastAPI):
  * RESTful API for projects and edits
  * SQLite database for metadata storage
  * Image processing pipeline with PIL/OpenCV
  * AI provider interface (pluggable)
  * Support for OpenAI, Stability AI, and mock providers
  * Feathered alpha blending for smooth compositing
  * Complete edit history tracking
  * File-based storage for images and edits

- Image Processing:
  * Patch extraction from bounding boxes
  * Mask generation for all selection types
  * Feathered edge blending
  * Patch compositing back to full image
  * No pixels modified outside selection
  * All edits reversible

- Infrastructure:
  * Docker Compose orchestration
  * Production and development configurations
  * Nginx reverse proxy for frontend
  * Hot-reload support for development
  * Volume persistence for data

Architecture follows specification exactly:
- Only selected regions are regenerated
- Full image pixels preserved outside mask
- Two-mode operation (cost vs quality)
- Complete edit history and reversibility
- Self-hosted with external AI API calls

All components are fully functional and ready for deployment.

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