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/coveringownmouth_ill_v1.json

@@ -2,35 +2,23 @@
   "action_id": "coveringownmouth_ill_v1",
   "action_name": "Coveringownmouth Ill V1",
   "action": {
-    "full_body": "character appearing sick or nauseous, posture slightly hunched forward",
-    "head": "pale complexion, sweatdrops on face, cheeks flushed or blue (if severe), grimacing",
-    "eyes": "tearing up, wincing, half-closed, or dilated pupils",
-    "arms": "one or both arms raised sharply towards the face",
-    "hands": "covering mouth, hand over mouth, fingers clutching face",
-    "torso": "leaning forward, tense shoulders usually associated with retching or coughing",
-    "pelvis": "neutral position or slightly bent forward",
-    "legs": "knees slightly bent or trembling",
-    "feet": "planted firmly or stumbling",
-    "additional": "motion lines indicating shaking, gloom lines, vomit (optional/extreme)"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "F"
+    "full_body": "character covering their mouth with their hand",
+    "head": "lower face obscured by hand",
+    "eyes": "neutral or expressive (depending on context)",
+    "arms": "arm raised towards face",
+    "hands": "hand placed over mouth, palm inward",
+    "torso": "upper body visible",
+    "pelvis": "variable",
+    "legs": "variable",
+    "feet": "variable",
+    "additional": "often indicates surprise, embarrassment, or silence"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/CoveringOwnMouth_Ill_V1.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "CoveringOwnMouth_Ill_V1"
+    "lora_triggers": "covering_own_mouth"
   },
   "tags": [
-    "covering mouth",
-    "hand over mouth",
-    "ill",
-    "sick",
-    "nausea",
-    "queasy",
-    "motion sickness",
-    "sweat",
-    "pale"
+    "covering_own_mouth"
   ]
 }