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/hugging_doggystyle_illustriousxl_lora_nochekaiser.json

@@ -2,34 +2,34 @@
   "action_id": "hugging_doggystyle_illustriousxl_lora_nochekaiser",
   "action_name": "Hugging Doggystyle Illustriousxl Lora Nochekaiser",
   "action": {
-    "full_body": "duo, 2 persons, doggystyle, from behind, all fours, intimate interaction",
-    "head": "looking back, head resting on shoulder, cheek to cheek, face buried in hair",
-    "eyes": "closed eyes, affectionate gaze, half-closed eyes",
-    "arms": "arms around waist, arms around neck, hugging, supporting body weight",
-    "hands": "hands on ground, hands clasping partner, grabbing sheets",
-    "torso": "arched back, bent over, chest pressed against back, leaning forward",
-    "pelvis": "kneeling, hips raised, bottom up",
-    "legs": "kneeling, bent knees, legs spread",
-    "feet": "barefoot, toes curled",
-    "additional": "sex from behind, affectionate, cuddling, romantic, indoor"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "doggystyle, all_fours, sex_from_behind",
+    "head": "blush, sweat, open_mouth",
+    "eyes": "rolled_eyes, closed_eyes",
+    "arms": "hug, hug_from_behind",
+    "hands": "hands_on_sheets",
+    "torso": "hanging_breasts, bent_over, trembling",
+    "pelvis": "hips",
+    "legs": "kneeling, spread_legs",
+    "feet": "toes",
+    "additional": "completely_nude, motion_lines, hetero, sex"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/hugging-doggystyle-illustriousxl-lora-nochekaiser.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "hugging-doggystyle-illustriousxl-lora-nochekaiser"
+    "lora_triggers": "hugging doggystyle, hug, doggystyle, sex_from_behind"
   },
   "tags": [
     "hugging_doggystyle",
+    "hug",
     "doggystyle",
-    "hugging",
-    "from behind",
-    "all fours",
-    "duo",
-    "intimate",
-    "kneeling"
+    "sex_from_behind",
+    "all_fours",
+    "hug_from_behind",
+    "hanging_breasts",
+    "trembling",
+    "sweat",
+    "open_mouth",
+    "completely_nude",
+    "motion_lines"
   ]
 }