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/cheekbulge.json

@@ -2,33 +2,29 @@
   "action_id": "cheekbulge",
   "action_name": "Cheekbulge",
   "action": {
-    "full_body": "kneeling, leaning forward, close-up focus on face",
-    "head": "visible cheek bulge, distorted cheek, stuffed mouth, mouth stretched",
-    "eyes": "looking up, upturned eyes, teary eyes, eye contact",
-    "arms": "reaching forward or resting on partner's legs",
-    "hands": "holding object, guiding, or resting on thighs",
-    "torso": "angled forward",
-    "pelvis": "neutral kneeling posture",
-    "legs": "kneeling, bent knees",
-    "feet": "toes pointing back",
-    "additional": "fellatio, oral sex, saliva, saliva trail, penis in mouth, face deformation"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "fellatio",
+    "head": "cheek_bulge, head_tilt, saliva",
+    "eyes": "looking_up",
+    "arms": "arms_behind_back",
+    "hands": "hands_on_head",
+    "torso": "upper_body",
+    "pelvis": "kneeling",
+    "legs": "kneeling",
+    "feet": "plantar_flexion",
+    "additional": "deepthroat, pov, penis"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/cheekbulge.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "cheekbulge"
+    "lora_triggers": "cheek bulge"
   },
   "tags": [
-    "cheek bulge",
-    "stuffed mouth",
+    "cheek_bulge",
+    "deepthroat",
     "fellatio",
-    "distorted face",
-    "oral sex",
-    "looking up",
-    "face deformation"
+    "saliva",
+    "head_tilt",
+    "penis",
+    "pov"
   ]
 }