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.

frontend/src/components/ImageCanvas.css

@@ -0,0 +1,28 @@
+.canvas-container {
+  position: relative;
+  width: 100%;
+  height: 100%;
+  min-height: 500px;
+  background-color: #2a2a2a;
+  border: 2px solid #444;
+  border-radius: 8px;
+  overflow: hidden;
+}
+
+.canvas-container canvas {
+  display: block;
+}
+
+.clear-selection-btn {
+  position: absolute;
+  top: 10px;
+  right: 10px;
+  background-color: #ff4444;
+  color: white;
+  padding: 8px 16px;
+  z-index: 10;
+}
+
+.clear-selection-btn:hover {
+  background-color: #cc0000;
+}