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/ilst.json

@@ -1,34 +1,32 @@
 {
   "action_id": "ilst",
-  "action_name": "Imminent Facesitting",
+  "action_name": "Ilst",
   "action": {
-    "full_body": "pov, facesitting",
-    "head": "",
-    "eyes": "",
-    "arms": "",
-    "hands": "",
-    "torso": "",
-    "pelvis": "pussy, pussy juice",
-    "legs": "",
-    "feet": "",
-    "additional": ""
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "F"
+    "full_body": "squatting or standing over the viewer, dominating the frame",
+    "head": "looking down at viewer",
+    "eyes": "looking at viewer",
+    "arms": "reaching towards viewer, one hand extending down",
+    "hands": "reaching or gesturing towards the camera",
+    "torso": "leaning forward slightly",
+    "pelvis": "centered in view, from below angle",
+    "legs": "straddling the viewer, wide stance",
+    "feet": "planted on ground",
+    "additional": "perspective from below, intimate proximity"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/ILST.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "ILST"
+    "lora_weight": 0.9,
+    "lora_triggers": "Facesitting_POV, from below"
   },
   "tags": [
-    "standing split",
-    "leg hold",
-    "high kick",
-    "gymnastics",
-    "yoga",
-    "stretching",
-    "balance"
+    "imminent_facesitting",
+    "pov",
+    "from_below",
+    "squatting",
+    "standing",
+    "looking_at_viewer",
+    "reaching_towards_viewer",
+    "legs_apart",
+    "solo"
   ]
 }