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/girl_b3dr00m_i.json

@@ -1,41 +1,39 @@
 {
   "scene_id": "girl_b3dr00m_i",
   "scene_name": "Girl B3Dr00M I",
-  "description": "A cozy, lived-in girl's bedroom filled with soft textures, personal items, and pastel decor.",
+  "description": "A beautifully designed modern bedroom with a warm and inviting atmosphere, featuring soft pastel tones, fairy lights, and a cozy bed.",
   "scene": {
-    "background": "indoors, bedroom, window, curtains, bookshelf, posters, wallpaper, ",
-    "foreground": "bed, pillows, stuffed toy, blanket, sheets, cushions",
+    "background": "indoors, bedroom, window, curtains, bookshelf, string_lights",
+    "foreground": "bed, pillow, blanket, potted_plant, bedside_table, cat",
     "furniture": [
       "bed",
-      "desk",
-      "chair",
-      "nightstand",
-      "rug",
-      "shelves"
+      "bookshelf",
+      "bedside_table"
     ],
     "colors": [
-      "pastel pink",
+      "pastel_colors",
       "white",
-      "cream",
-      "light blue",
-      "lavender"
+      "brown"
     ],
-    "lighting": "soft natural light, sunlight, bright, ambient occlusion",
-    "theme": "cozy, cute, kawaii,interior"
+    "lighting": "sunlight, warm_light, volumetric_lighting",
+    "theme": "cozy, modern, scenery"
   },
   "lora": {
     "lora_name": "Illustrious/Backgrounds/Girl_b3dr00m-i.safetensors",
-    "lora_weight": 0.7,
-    "lora_triggers": "Girl_b3dr00m-i"
+    "lora_weight": 1.0,
+    "lora_triggers": "Girl b3dr00m"
   },
   "tags": [
     "indoors",
     "bedroom",
-    "scenery",
-    "no humans",
     "room",
+    "scenery",
+    "no_humans",
+    "bed",
     "furniture",
-    "messy",
-    "pastel colors"
+    "window",
+    "curtains",
+    "string_lights",
+    "pastel_colors"
   ]
 }