Add Checkpoints Gallery with per-checkpoint generation settings

- New Checkpoint model (slug, name, checkpoint_path, data JSON, image_path)
- sync_checkpoints() loads metadata from data/checkpoints/*.json and falls
  back to template defaults for models without a JSON file
- _apply_checkpoint_settings() applies per-checkpoint steps, CFG, sampler,
  base positive/negative prompts, and VAE (with dynamic VAELoader node
  injection for non-integrated VAEs) to the ComfyUI workflow
- Bulk Create from Checkpoints: scans Illustrious/Noob model directories,
  reads matching HTML files, uses LLM to populate metadata, falls back to
  template defaults when no HTML is present
- Gallery index with batch cover generation and WebSocket progress bar
- Detail page showing Generation Settings and Base Prompts cards
- Checkpoints nav link added to layout
- New data/prompts/checkpoint_system.txt LLM system prompt
- Updated README with all current galleries and file structure
- Also includes accumulated action/scene JSON updates, new actions, and
  other template/generator improvements from prior sessions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

models.py

@@ -99,10 +99,25 @@ class Detailer(db.Model):
     def __repr__(self):
         return f'<Detailer {self.detailer_id}>'
 
+class Checkpoint(db.Model):
+    id = db.Column(db.Integer, primary_key=True)
+    checkpoint_id = db.Column(db.String(255), unique=True, nullable=False)
+    slug = db.Column(db.String(255), unique=True, nullable=False)
+    name = db.Column(db.String(255), nullable=False)
+    checkpoint_path = db.Column(db.String(255), nullable=False)  # e.g. "Illustrious/model.safetensors"
+    data = db.Column(db.JSON, nullable=True)
+    image_path = db.Column(db.String(255), nullable=True)
+
+    def __repr__(self):
+        return f'<Checkpoint {self.checkpoint_id}>'
+
 class Settings(db.Model):
     id = db.Column(db.Integer, primary_key=True)
+    llm_provider = db.Column(db.String(50), default='openrouter') # 'openrouter', 'ollama', 'lmstudio'
     openrouter_api_key = db.Column(db.String(255), nullable=True)
     openrouter_model = db.Column(db.String(100), default='google/gemini-2.0-flash-001')
+    local_base_url = db.Column(db.String(255), nullable=True)
+    local_model = db.Column(db.String(100), nullable=True)
 
     def __repr__(self):
         return '<Settings>'