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/chokehold.json

@@ -2,38 +2,34 @@
   "action_id": "chokehold",
   "action_name": "Chokehold",
   "action": {
-    "full_body": "dynamic combat pose, character positioning behind an opponent, executing a rear chokehold, two people grappling",
-    "head": "chin tucked tight, face pressed close to the opponent's head, intense or straining expression",
-    "eyes": "focused, narrowed in concentration",
-    "arms": "one arm wrapped tightly around the opponent's neck, the other arm locking the hold by gripping the bicep or clasping hands",
-    "hands": "clenching tight, gripping own bicep or locking fingers behind opponent's neck",
-    "torso": "chest pressed firmly against the opponent's back, leaning back slightly for leverage",
-    "pelvis": "pressed close to opponent's lower back",
-    "legs": "wrapped around the opponent's waist (body triangle or hooks in) or wide standing stance for stability",
-    "feet": "hooked inside opponent's thighs or planted firmly on the ground",
-    "additional": "struggle, tension, submission hold, restrictive motion, self-defense scenario"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "rear_naked_choke, from_behind, struggling, kneeling",
+    "head": "head_back, expressionless, open_mouth",
+    "eyes": "rolling_eyes, tearing_up, empty_eyes",
+    "arms": "arm_around_neck, struggling, grabbing_arm",
+    "hands": "clenched_hands, struggling",
+    "torso": "leaning_forward, arched_back",
+    "pelvis": "kneeling, bent_over",
+    "legs": "kneeling, spread_legs",
+    "feet": "barefoot, toes_curled",
+    "additional": "distress, blushing, saliva, veins"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/chokehold.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "chokehold"
+    "lora_triggers": "choke hold"
   },
   "tags": [
-    "chokehold",
-    "grappling",
-    "rear naked choke",
-    "fighting",
-    "wrestling",
-    "martial arts",
-    "restraining",
-    "submission",
-    "headlock",
-    "strangle",
-    "duo",
-    "struggle"
+    "choke_hold",
+    "rear_naked_choke",
+    "strangling",
+    "arm_around_neck",
+    "from_behind",
+    "struggling",
+    "head_back",
+    "clenched_teeth",
+    "rolling_eyes",
+    "drooling",
+    "saliva",
+    "ohogao"
   ]
 }