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/tinygirl___illustrious_000016.json

@@ -2,34 +2,27 @@
   "action_id": "tinygirl___illustrious_000016",
   "action_name": "Tinygirl Illustrious 000016",
   "action": {
-    "full_body": "sitting, knees up, embracing knees, small scale",
-    "head": "tilted up, looking up",
-    "eyes": "wide eyes, curious",
-    "arms": "arms around legs",
-    "hands": "hands clasped",
-    "torso": "leaning forward slightly",
-    "pelvis": "sitting on surface",
-    "legs": "bent, knees to chest",
-    "feet": "close together",
-    "additional": "size difference, giant surroundings, depth of field, oversized furniture"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "minigirl, size_difference, standing",
+    "head": "looking_at_viewer, looking_up",
+    "eyes": "detailed_eyes",
+    "arms": "arms_at_sides",
+    "hands": "small_hands",
+    "torso": "torso",
+    "pelvis": "hips",
+    "legs": "legs_together",
+    "feet": "barefoot",
+    "additional": "giant, miniature, scale_comparison, high_angle"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Tinygirl_-_Illustrious-000016.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Tinygirl_-_Illustrious-000016"
+    "lora_weight": 0.6,
+    "lora_triggers": "teeny, tinygirl"
   },
   "tags": [
-    "tinygirl",
-    "size difference",
-    "mini",
-    "sitting",
-    "knees up",
-    "looking up",
-    "giant background",
-    "macrophilia"
+    "minigirl",
+    "size_difference",
+    "1girl",
+    "miniature",
+    "looking_at_viewer"
   ]
 }