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/cozy_bedroom___illustrious.json

@@ -1,35 +1,37 @@
 {
   "scene_id": "cozy_bedroom___illustrious",
   "scene_name": "Cozy Bedroom Illustrious",
-  "description": "A warm and inviting bedroom filled with soft light, plush textures, and a relaxing atmosphere.",
+  "description": "A detailed, modern, and lived-in cozy bedroom environment with scattered items and warm atmosphere.",
   "scene": {
-    "background": "indoors, bedroom, window, white curtains, sunlight, wood floor, bookshelf, potted plant, cluttered",
-    "foreground": "bed, messy bed, white bed sheet, duvet, pile of pillows, plush toy, blanket",
+    "background": "indoors, bedroom, house, scenery, window, curtains, wooden_floor, messy_room",
+    "foreground": "potted_plant, desk, chair, computer",
     "furniture": [
-      "double bed",
-      "nightstand",
-      "rug",
-      "desk"
+      "bed",
+      "desk",
+      "bookshelf",
+      "chair",
+      "lamp",
+      "pillow",
+      "blanket"
     ],
     "colors": [
-      "beige",
-      "warm brown",
-      "cream",
-      "pastel yellow"
+      "brown_theme",
+      "orange_theme"
     ],
-    "lighting": "warm lighting, natural light, soft illumination, afternoon sun",
-    "theme": "cozy, comfort, slice of life, relaxation"
+    "lighting": "sunlight, sunbeam, light_rays, dim_lighting",
+    "theme": "anime_coloring"
   },
   "lora": {
     "lora_name": "Illustrious/Backgrounds/Cozy_bedroom_-_Illustrious.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Cozy_bedroom_-_Illustrious"
+    "lora_weight": 0.8,
+    "lora_triggers": "cozybedroom"
   },
   "tags": [
-    "scenery",
-    "no humans",
+    "modern",
+    "cozy",
     "interior",
-    "highly detailed",
-    "aesthetic"
+    "morning",
+    "bright",
+    "dutch_angle"
   ]
 }