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/app/main.py

@@ -0,0 +1,53 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.staticfiles import StaticFiles
+from contextlib import asynccontextmanager
+
+from app.config import settings
+from app.database import init_db
+from app.routers import projects, edits, images
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Initialize database on startup"""
+    init_db()
+    yield
+
+
+app = FastAPI(
+    title="AI Photo Edit API",
+    description="API for AI-powered photo editing with mask-scoped regeneration",
+    version="1.0.0",
+    lifespan=lifespan
+)
+
+# Configure CORS
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=settings.cors_origins_list,
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# Include routers
+app.include_router(projects.router)
+app.include_router(edits.router)
+app.include_router(images.router)
+
+
+@app.get("/")
+def root():
+    """API root endpoint"""
+    return {
+        "name": "AI Photo Edit API",
+        "version": "1.0.0",
+        "status": "running"
+    }
+
+
+@app.get("/health")
+def health():
+    """Health check endpoint"""
+    return {"status": "healthy"}