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/covering_privates_illustrious_v1_0.json

@@ -2,34 +2,29 @@
   "action_id": "covering_privates_illustrious_v1_0",
   "action_name": "Covering Privates Illustrious V1 0",
   "action": {
-    "full_body": "standing in a defensive, modest posture, body language expressing vulnerability",
-    "head": "tilted down or looking away in embarrassment",
-    "eyes": "averted gaze, shy or flustered expression",
-    "arms": "arms pulled in tight against the body",
-    "hands": "hands covering crotch, hand over breasts, covering self",
-    "torso": "slightly hunched forward or twisting away",
-    "pelvis": "hips slightly turned",
-    "legs": "legs pressed tightly together, thighs touching, knock-kneed",
-    "feet": "standing close together, possibly pigeon-toed",
-    "additional": "blush, steam or light rays (optional)"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "F"
+    "full_body": "covering_privates",
+    "head": "embarrassed, blush",
+    "eyes": "looking_at_viewer",
+    "arms": "arm_across_chest",
+    "hands": "covering_breasts, covering_crotch",
+    "torso": "upper_body",
+    "pelvis": "hips",
+    "legs": "legs_together",
+    "feet": "standing",
+    "additional": "modesty"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/covering privates_illustrious_V1.0.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "covering privates_illustrious_V1.0"
+    "lora_triggers": "covering privates, covering crotch, covering breasts"
   },
   "tags": [
-    "covering self",
+    "covering_privates",
+    "covering_breasts",
+    "covering_crotch",
     "embarrassed",
     "blush",
-    "hands on crotch",
-    "arm across chest",
-    "modesty",
-    "legs together",
-    "shy"
+    "arm_across_chest",
+    "legs_together"
   ]
 }