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/sitting_on_mouth_000012_illustrious.json

@@ -2,34 +2,31 @@
   "action_id": "sitting_on_mouth_000012_illustrious",
   "action_name": "Sitting On Mouth 000012 Illustrious",
   "action": {
-    "full_body": "sitting directly on top of camera, straddling position, pov from below, squatting or kneeling",
-    "head": "tilted down, looking down at viewer",
-    "eyes": "looking at viewer, eye contact",
-    "arms": "resting on knees or supporting weight on bed/floor",
-    "hands": "hands on knees, grabbing thighs, or caressing own legs",
-    "torso": "foward leaning, foreshortened perspective",
-    "pelvis": "centered in view, pressing down",
-    "legs": "spread legs, knees bent, thighs framing the image",
-    "feet": "planted on surface on either side of viewer or out of frame",
-    "additional": "intimate proximity, focus on thighs and hips, view from bottom"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "sitting_on_face, sitting_on_person, femdom",
+    "head": "looking_down, dominant_expression",
+    "eyes": "looking_at_viewer, narrowing_eyes",
+    "arms": "arms_at_sides",
+    "hands": "resting_on_legs",
+    "torso": "leaning_forward",
+    "pelvis": "sitting",
+    "legs": "outstretched_legs, spread_legs, legs_apart",
+    "feet": "barefoot",
+    "additional": "1boy, lying_on_back, choking"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Sitting_On_Mouth-000012 Illustrious.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "Sitting_On_Mouth-000012 Illustrious"
+    "lora_triggers": "FSOMILV1, facesitting, femdom"
   },
   "tags": [
-    "facesitting",
-    "sitting on face",
-    "pov",
-    "from below",
-    "straddling",
-    "looking down",
-    "thighs",
-    "crotch focus"
+    "sitting_on_face",
+    "sitting_on_person",
+    "outstretched_legs",
+    "spread_legs",
+    "looking_down",
+    "femdom",
+    "full_body",
+    "dominant_female",
+    "legs_apart"
   ]
 }