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>

data/actions/superstyle_illustrious.json

@@ -2,31 +2,34 @@
   "action_id": "superstyle_illustrious",
   "action_name": "Superstyle Illustrious",
   "action": {
-    "full_body": "dynamic full body shot, exaggerated perspective, dutch angle, floating pose or action stance",
-    "head": "confident expression, facing viewer, hair flowing dynamically",
-    "eyes": "sharp focus, detailed eyes, intense gaze",
-    "arms": "reaching towards camera or spread wide",
-    "hands": "fingers splayed, dramatic gesture",
-    "torso": "slightly twisted, leaning forward or backward",
-    "pelvis": "tilted hips",
-    "legs": "foreshortened, one leg extended towards viewer",
-    "feet": "dynamic positioning",
-    "additional": "wind effects, cinematic lighting, high contrast, vibrant colors, sharp outlines"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "doggystyle, all_fours, kneeling, sex_from_behind",
+    "head": "blush, clenched_teeth",
+    "eyes": "half_closed_eyes",
+    "arms": "arms_extended_forward",
+    "hands": "hands_on_ground",
+    "torso": "bent_over, arched_back, hanging_breasts",
+    "pelvis": "raised_hips, ass, presenting_hindquarters",
+    "legs": "kneeling, spread_legs",
+    "feet": "toes",
+    "additional": "size_difference, interspecies, from_side, sex"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Superstyle_Illustrious.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Superstyle_Illustrious"
+    "lora_weight": 0.7,
+    "lora_triggers": "superstyle"
   },
   "tags": [
-    "dynamic pose",
-    "intricate details",
-    "stylized",
-    "masterpiece",
-    "vibrant"
+    "doggystyle",
+    "all_fours",
+    "sex_from_behind",
+    "from_side",
+    "arched_back",
+    "raised_hips",
+    "bent_over",
+    "hands_on_ground",
+    "hanging_breasts",
+    "interspecies",
+    "size_difference",
+    "blush"
   ]
 }