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/scenes/vip.json

@@ -1,35 +1,40 @@
 {
   "scene_id": "vip",
   "scene_name": "Vip",
-  "description": "A high-end, exclusive VIP lounge scene set in a luxury penthouse overlooking a city skyline at night.",
+  "description": "An exclusive, dimly lit VIP area in a bustling nightclub, separated by velvet rope stanchions and furnished with plush couches and tables laden with expensive alcohol and money.",
   "scene": {
-    "background": "indoors, penthouse, luxury, cityscape, night, skyline, large window, heavy curtains, golden geometric patterns",
-    "foreground": "champagne bottle, ice bucket, crystal glasses, velvet rope, red carpet",
+    "background": "nightclub, indoors, dim_lighting",
+    "foreground": "stanchion, alcohol, drinking_glass, banknote, money",
     "furniture": [
-      "chesterfield sofa",
-      "crystal chandelier",
-      "marble coffee table",
-      "gold accents"
+      "couch",
+      "booth_seating",
+      "table"
     ],
     "colors": [
-      "gold",
-      "black",
-      "burgundy",
-      "royal purple"
+      "red",
+      "purple",
+      "black"
     ],
-    "lighting": "dim lighting, mood lighting, cinematic, soft glow, city lights",
-    "theme": "luxury, wealth, exclusivity, nightlife"
+    "lighting": "neon_lights",
+    "theme": "party"
   },
   "lora": {
     "lora_name": "Illustrious/Backgrounds/VIP.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "VIP"
+    "lora_weight": 0.7,
+    "lora_triggers": "v1p"
   },
   "tags": [
-    "vip",
-    "luxury",
-    "rich",
-    "elegant",
-    "high lass"
+    "nightclub",
+    "indoors",
+    "stanchion",
+    "couch",
+    "table",
+    "alcohol",
+    "drinking_glass",
+    "booth_seating",
+    "money",
+    "banknote",
+    "neon_lights",
+    "dim_lighting"
   ]
 }