Add Replicate provider, model selection, and Patch Library features

Major additions:
1. Replicate AI Provider
   - Support for multiple models (SDXL, LaMa, Realistic Vision)
   - Auto-model selection based on prompt keywords
   - Best for human features: realistic-vision (~$0.020/image)
   - Best for removal: lama (~$0.002/image)
   - Best general purpose: sdxl-inpaint (~$0.025/image)
   - Smart keyword detection for automatic model selection

2. Enhanced Stability AI Provider
   - Optimized parameters for better quality
   - Support for multiple engines (SDXL, SD 1.5, SD 2.1)
   - Increased steps and CFG scale for improved results

3. Model Selection System
   - Per-edit model override capability
   - Global default model configuration
   - Provider-specific model options
   - Auto-selection based on prompt analysis

4. Patch Library Feature
   - Save AI-generated patches for reuse
   - Save manually selected regions
   - Import external images as patches
   - Organize with categories and tags
   - Browse and filter patch library
   - Apply saved patches to new images
   - Thumbnail generation for quick preview
   - Cost savings by reusing good results

5. Comprehensive Documentation
   - MODEL_SELECTION_GUIDE.md: Detailed guide for choosing models
     * Best models for hands, faces, bodies
     * Quality comparison table
     * Cost optimization strategies
     * Troubleshooting common issues
   - QUICK_START.md: How-to guide for new features
     * Model selection examples
     * Patch library workflow
     * API reference
     * Pro tips and cost comparisons

6. Configuration Updates
   - Added Replicate API key support
   - Model selection settings
   - Per-edit override toggle
   - Updated .env.example with all options

Benefits:
- Better quality for human features (hands, faces)
- 90% cost reduction using lama for removals
- Reusable patch library saves money and ensures consistency
- Auto-model selection optimizes quality and cost
- Flexibility to choose provider and model per edit

All backend changes are fully functional and ready for use.
Frontend UI for patch library pending.

backend/app/schemas.py

@@ -68,6 +68,45 @@ class UploadResponse(BaseModel):
     current_url: str
 
 
+# Patch Library schemas
+class PatchCreate(BaseModel):
+    name: str
+    description: Optional[str] = None
+    source_type: str  # "ai_generated", "manual_selection", "imported"
+    source_project_id: Optional[int] = None
+    source_edit_id: Optional[int] = None
+    category: Optional[str] = None
+    tags: Optional[str] = None
+    bbox: Optional[Dict[str, int]] = None
+
+
+class PatchResponse(BaseModel):
+    id: int
+    name: str
+    description: Optional[str]
+    created_at: datetime
+    source_type: str
+    source_project_id: Optional[int]
+    source_edit_id: Optional[int]
+    width: int
+    height: int
+    tags: Optional[str]
+    category: Optional[str]
+    is_public: bool
+    file_path: str
+    thumbnail_path: Optional[str]
+
+    class Config:
+        from_attributes = True
+
+
+class PatchApply(BaseModel):
+    project_id: int
+    patch_id: int
+    bbox: Dict[str, int]
+    feather_px: int = 5
+
+
 # Generic responses
 class StatusResponse(BaseModel):
     status: str