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/spread_pussy_one_hand_pony_v1_0.json

@@ -2,36 +2,30 @@
   "action_id": "spread_pussy_one_hand_pony_v1_0",
   "action_name": "Spread Pussy One Hand Pony V1 0",
   "action": {
-    "full_body": "lying on back, legs spread wide, lower body focus",
-    "head": "tilted forward, looking at viewer",
-    "eyes": "aroused, half-closed eyes, heart-shaped pupils",
-    "arms": "one arm reaching down between legs, other arm resting at side",
-    "hands": "one hand on crotch, fingers spreading pussy, spreading labia",
-    "torso": "arched back, navel exposed",
-    "pelvis": "hips wide, genitals exposed, vulva visible",
-    "legs": "legs apart, m-legs, knees bent",
-    "feet": "toes curled",
-    "additional": "pussy juice, wet, detailed, uncensored"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "spread_legs, m_legs, legs_up",
+    "head": "looking_at_viewer, blush",
+    "eyes": "open_eyes",
+    "arms": "arms_apart",
+    "hands": "fingering",
+    "torso": "exposed_breasts, navel",
+    "pelvis": "spread_pussy, kupaa, cameltoe",
+    "legs": "spread_legs, m_legs, legs_apart",
+    "feet": "barefoot",
+    "additional": "pussy_juice"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/spread pussy one hand_pony_V1.0.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "spread pussy one hand_pony_V1.0"
+    "lora_triggers": "spread pussy, one hand"
   },
   "tags": [
-    "spread pussy",
-    "one hand",
-    "spreading",
-    "pussy",
-    "open legs",
-    "vaginal",
+    "spread_pussy",
+    "kupaa",
+    "spread_legs",
+    "m_legs",
+    "legs_apart",
+    "legs_up",
     "fingering",
-    "genitals",
-    "uncensored",
-    "lower body"
+    "looking_at_viewer"
   ]
 }