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/models/__init__.py

@@ -1,5 +1,6 @@
 from app.models.user import User
 from app.models.project import Project
 from app.models.edit import Edit
+from app.models.patch import Patch
 
-__all__ = ["User", "Project", "Edit"]
+__all__ = ["User", "Project", "Edit", "Patch"]

backend/app/models/patch.py

@@ -0,0 +1,37 @@
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, Text, Boolean
+from sqlalchemy.orm import relationship
+from datetime import datetime
+from app.database import Base
+
+
+class Patch(Base):
+    __tablename__ = "patches"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
+    name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+
+    # Source information
+    source_type = Column(String, nullable=False)  # "ai_generated", "manual_selection", "imported"
+    source_project_id = Column(Integer, ForeignKey("projects.id"), nullable=True)
+    source_edit_id = Column(Integer, ForeignKey("edits.id"), nullable=True)
+
+    # Patch metadata
+    width = Column(Integer, nullable=False)
+    height = Column(Integer, nullable=False)
+    tags = Column(Text, nullable=True)  # Comma-separated tags
+    category = Column(String, nullable=True)  # "hand", "face", "body", "object", "texture", etc.
+
+    # Is this patch shared/public?
+    is_public = Column(Boolean, default=False)
+
+    # File path (relative to data dir)
+    file_path = Column(String, nullable=False)
+    thumbnail_path = Column(String, nullable=True)
+
+    # Relationships
+    user = relationship("User", back_populates="patches")
+    source_project = relationship("Project")
+    source_edit = relationship("Edit")

backend/app/models/user.py

@@ -14,3 +14,4 @@ class User(Base):
 
     # Relationships
     projects = relationship("Project", back_populates="user", cascade="all, delete-orphan")
+    patches = relationship("Patch", back_populates="user", cascade="all, delete-orphan")