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/pantygag.json

@@ -2,36 +2,35 @@
   "action_id": "pantygag",
   "action_name": "Pantygag",
   "action": {
-    "full_body": "kneeling or sitting in a restrained posture",
-    "head": "panties stuffed into open mouth, fabric wrapped around lower face, cheeks bulging",
-    "eyes": "wide open, slightly tearing or looking up in embarrassment",
-    "arms": "positioned behind the back",
-    "hands": "wrists bound together",
-    "torso": "slightly arched, chest forward",
-    "pelvis": "hips stationary, taking weight if sitting",
-    "legs": "knees bent, shins touching the ground",
-    "feet": "toes pointing backward or feet crossed",
-    "additional": "detailed fabric texture of the underwear used as a gag"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "upper_body",
+    "head": "panty_gag, panties_in_mouth, open_mouth, saliva, drooling, spit, tongue_out",
+    "eyes": "hypnosis, @_@",
+    "arms": "hands_on_own_cheeks, cheek_pinching",
+    "hands": "fingers_on_face",
+    "torso": "string",
+    "pelvis": "string",
+    "legs": "string",
+    "feet": "string",
+    "additional": "panty_gag, panties_in_mouth"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/pantygag.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "pantygag"
+    "lora_triggers": "panty gag"
   },
   "tags": [
-    "pantygag",
-    "panties in mouth",
-    "gagged",
-    "open mouth",
-    "bulging cheeks",
-    "kneeling",
-    "bound wrists",
-    "restrained",
-    "flushed face",
-    "drool"
+    "panty_gag",
+    "panties_in_mouth",
+    "saliva",
+    "drooling",
+    "spit",
+    "hypnosis",
+    "@_@",
+    "cheek_pinching",
+    "hands_on_own_cheeks",
+    "tongue_out",
+    "open_mouth",
+    "bdsm",
+    "gag"
   ]
 }