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/lotusposition.json

@@ -2,36 +2,30 @@
   "action_id": "lotusposition",
   "action_name": "Lotusposition",
   "action": {
-    "full_body": "sitting in lotus position, padmasana, meditative posture, yoga pose, whole body visible",
-    "head": "facing forward, calm expression, chin slightly tucked",
-    "eyes": "closed eyes, relaxing, or soft gaze downwards",
-    "arms": "arms relaxed, wrists resting on knees, elbows slightly bent",
-    "hands": "gyan mudra, index fingers touching thumbs, palms facing up, open hands",
-    "torso": "posture erect, straight spine, chest open, upright",
-    "pelvis": "grounded, sitting on floor, hips externally rotated",
-    "legs": "crossed legs tightly, feet resting on opposite thighs, flexibility",
-    "feet": "soles facing upward, feet visible on thighs, barefoot",
-    "additional": "serene atmosphere, tranquility, zen, spiritual practice"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "lotus_position, sitting",
+    "head": "facing_viewer",
+    "eyes": "closed_eyes",
+    "arms": "arms_at_sides",
+    "hands": "hands_on_lap, mudra",
+    "torso": "upper_body",
+    "pelvis": "hips",
+    "legs": "crossed_legs",
+    "feet": "soles, barefoot",
+    "additional": "meditation, yoga, floating_hair"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/lotusposition.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "lotusposition"
+    "lora_triggers": "lotus position"
   },
   "tags": [
-    "lotus position",
+    "lotus_position",
+    "sitting",
+    "crossed_legs",
     "meditation",
     "yoga",
-    "sitting",
-    "padmasana",
-    "crossed legs",
-    "zen",
-    "peaceful",
-    "flexible",
-    "barefoot"
+    "soles",
+    "barefoot",
+    "hands_on_lap"
   ]
 }