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/sgb_ilxl_v1.json

@@ -2,34 +2,30 @@
   "action_id": "sgb_ilxl_v1",
   "action_name": "Sgb Ilxl V1",
   "action": {
-    "full_body": "character performing a vertical standing split (I-balance), standing on one leg with the other extended straight up",
-    "head": "upright, facing forward",
-    "eyes": "looking at viewer",
-    "arms": "reaching upwards to support the lifted leg",
-    "hands": "grasping the ankle, foot, or calf of the vertical leg",
-    "torso": "erect, maintaining balance",
-    "pelvis": "tilted upward to allow the leg to reach vertical extension",
-    "legs": "one leg planted firmly on the ground, the other lifted 180 degrees vertically alongside the head",
-    "feet": "raised foot pointed towards the sky",
-    "additional": "demonstrating extreme flexibility and gymnastics ability"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "upper_body",
+    "head": "blush, smile, open_mouth",
+    "eyes": "looking_at_viewer",
+    "arms": "arms_on_breasts",
+    "hands": "grabbing_own_breast",
+    "torso": "medium_breasts, breast_squeeze",
+    "pelvis": "n/a",
+    "legs": "n/a",
+    "feet": "n/a",
+    "additional": "fingers, skin_indentation"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/sgb_ilxl_v1.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "sgb_ilxl_v1"
+    "lora_triggers": "grabbing another's breast, grabbing own breast"
   },
   "tags": [
-    "standing split",
-    "i-balance",
-    "holding leg",
-    "leg up",
-    "high kick",
-    "stretching",
-    "gymnastics",
-    "flexible"
+    "grabbing_own_breast",
+    "grabbing_another's_breast",
+    "groping",
+    "squeezing",
+    "medium_breasts",
+    "large_breasts",
+    "rubbing_breasts",
+    "close-up"
   ]
 }