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/illustriousxl_size_difference_large_female.json

@@ -2,33 +2,32 @@
   "action_id": "illustriousxl_size_difference_large_female",
   "action_name": "Illustriousxl Size Difference Large Female",
   "action": {
-    "full_body": "towering female figure standing over a tiny environment or person, emphasizing extreme scale difference",
-    "head": "tilted downwards, looking down with curiosity or affection",
-    "eyes": "gazing intently at the object in hand or on the ground",
-    "arms": "elbows bent, lifting one hand closer to the face for inspection",
-    "hands": "palm open and facing up, cupping a tiny person or object gently",
-    "torso": "leaning slightly forward to reduce the distance to the smaller subject",
-    "pelvis": "neutral standing posture, hips slightly shifted",
-    "legs": "standing firm and pillar-like to emphasize stability and size",
-    "feet": "planted firmly on the ground, perhaps next to tiny buildings or trees for scale comparison",
-    "additional": "low angle view, depth of field, giantess theme, macro perspective on hand"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "standing, size_difference, height_difference, giantess, mini_person, duo",
+    "head": "looking_down, looking_at_another",
+    "eyes": "open_eyes",
+    "arms": "arms_at_sides",
+    "hands": "hands_down",
+    "torso": "upper_body, leaning_forward",
+    "pelvis": "hips",
+    "legs": "standing, long_legs",
+    "feet": "standing",
+    "additional": "low_angle, man_looking_up"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/IllustriousXL_Size_difference_large_female.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "IllustriousXL_Size_difference_large_female"
+    "lora_triggers": "size difference, larger female, smaller male, tall female"
   },
   "tags": [
-    "size difference",
+    "size_difference",
     "giantess",
-    "looking down",
-    "holding tiny person",
-    "perspective",
-    "interaction",
-    "scale comparison"
+    "height_difference",
+    "tall_female",
+    "larger_female",
+    "mini_person",
+    "looking_down",
+    "looking_up",
+    "looking_at_another",
+    "standing"
   ]
 }