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/bodybengirl.json

@@ -2,32 +2,29 @@
   "action_id": "bodybengirl",
   "action_name": "Bodybengirl",
   "action": {
-    "full_body": "character standing and bending forward at the waist, hips raised high",
-    "head": "looking back at viewer or head inverted",
-    "eyes": "looking at viewer",
-    "arms": "extended downwards towards the ground",
-    "hands": "touching toes, ankles, or palms flat on the floor",
-    "torso": "upper body folded down parallel to or against the legs",
-    "pelvis": "lifted upwards, prominent posterior view",
-    "legs": "straight or knees slightly locked, shoulder-width apart",
-    "feet": "planted firmly on the ground",
-    "additional": "often viewed from behind or the side to emphasize flexibility and curve"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "suspended_congress, lifting_person, standing",
+    "head": "",
+    "eyes": "",
+    "arms": "reaching",
+    "hands": "",
+    "torso": "torso_grab, bent_over",
+    "pelvis": "",
+    "legs": "legs_hanging",
+    "feet": "",
+    "additional": "1boy, 1girl, suspended"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/BodyBenGirl.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "BodyBenGirl"
+    "lora_triggers": "bentstand-front, bentstand-behind"
   },
   "tags": [
-    "bending over",
-    "touching toes",
-    "from behind",
-    "flexibility",
+    "suspended_congress",
+    "torso_grab",
+    "bent_over",
+    "reaching",
     "standing",
-    "jack-o' pose"
+    "1boy",
+    "1girl"
   ]
 }