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/facesit_08.json

@@ -2,33 +2,36 @@
   "action_id": "facesit_08",
   "action_name": "Facesit 08",
   "action": {
-    "full_body": "POV perspective from below, character straddling the camera/viewer in a squatting or kneeling position",
-    "head": "tilted downwards, looking directly at the viewer",
-    "eyes": "gazing down, maintaining eye contact",
-    "arms": "resting comfortably",
-    "hands": "placed on own thighs or knees for support",
-    "torso": "foreshortened from below, leaning slightly forward",
-    "pelvis": "positioned directly over the camera lens, dominating the frame",
-    "legs": "spread wide, knees bent deeply, thighs framing the view",
-    "feet": "resting on the surface on either side of the viewpoint",
-    "additional": "extreme low angle, forced perspective, intimate proximity"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "sitting_on_face, cunnilingus, oral",
+    "head": "looking_at_viewer, looking_down",
+    "eyes": "looking_at_viewer",
+    "arms": "head_grab",
+    "hands": "on_head",
+    "torso": "nude, close-up",
+    "pelvis": "panties_aside, clitoris, pussy_juice",
+    "legs": "spread_legs",
+    "feet": "out_of_frame",
+    "additional": "yuri, female_pov, 2girls"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/facesit-08.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "facesit-08"
+    "lora_weight": 0.8,
+    "lora_triggers": "2girls, female pov, close-up, looking at viewer, sitting on face, oral, cunnilingus, spread legs, pussy juice, clitoris"
   },
   "tags": [
-    "facesitting",
-    "pov",
-    "femdom",
-    "squatting",
-    "looking down",
-    "low angle",
-    "thighs"
+    "2girls",
+    "female_pov",
+    "close-up",
+    "looking_at_viewer",
+    "sitting_on_face",
+    "oral",
+    "cunnilingus",
+    "spread_legs",
+    "pussy_juice",
+    "clitoris",
+    "yuri",
+    "panties_aside",
+    "head_grab",
+    "looking_down"
   ]
 }