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/fixed_point_v2.json

@@ -2,33 +2,30 @@
   "action_id": "fixed_point_v2",
   "action_name": "Fixed Point V2",
   "action": {
-    "full_body": "standing, assertive posture, foreshortening effect on the arm",
-    "head": "facing viewer, chin slightly tucked or tilted confidentially",
-    "eyes": "looking at viewer, focused gaze, winking or intense stare",
-    "arms": "arm extended forward towards the camera, elbow straight or slightly bent",
-    "hands": "finger gun, pointing, index finger extended, thumb raised, hand gesture",
-    "torso": "facing forward, slight rotation to align with the pointing arm",
-    "pelvis": "neutral standing position",
-    "legs": "standing, hip width apart",
-    "feet": "grounded",
-    "additional": "depth of field, focus on hand, perspective usually from front"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "kneeling on floor in bedroom",
+    "head": "looking at viewer",
+    "eyes": "open eyes",
+    "arms": "resting on bed",
+    "hands": "resting",
+    "torso": "facing viewer",
+    "pelvis": "kneeling",
+    "legs": "kneeling",
+    "feet": "barefoot",
+    "additional": "full room view, fxdpt"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/fixed_point_v2.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "fixed_point_v2"
+    "lora_weight": 0.8,
+    "lora_triggers": "fxdpt, full room view"
   },
   "tags": [
-    "gesture",
-    "finger gun",
-    "pointing",
-    "aiming",
-    "looking at viewer",
-    "foreshortening",
-    "bang"
+    "kneeling",
+    "on_floor",
+    "indoors",
+    "bedroom",
+    "bed",
+    "wide_shot",
+    "from_above",
+    "perspective"
   ]
 }