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/barbie_b3dr00m_i.json

@@ -1,39 +1,49 @@
 {
   "scene_id": "barbie_b3dr00m_i",
   "scene_name": "Barbie B3Dr00M I",
-  "description": "A vibrant and glamorous bedroom inspired by a Barbie dream house, featuring extensive pink decor, plastic-like textures, and cute, girly aesthetics typical of a dollhouse interior.",
+  "description": "A vibrant, pink-themed Barbie bedroom filled with glamorous decor and accessories.",
   "scene": {
-    "background": "indoors, bedroom, pink wallpaper, heart pattern, window, lace curtains, chandelier, ornate walls",
-    "foreground": "bed, pink bedding, fluffy pillows, stuffed toys, perfume bottles, vanity mirror",
+    "background": "indoors, bedroom, pink_theme, neon_lights, curtains, wall, shelf",
+    "foreground": "bed, pillow, handbag, high_heels, tiara, sequins, gem, ribbon",
     "furniture": [
-      "canopy bed",
-      "vanity table",
-      "heart-shaped chair",
-      "wardrobe",
-      "nightstand"
+      "bed",
+      "chandelier",
+      "mirror",
+      "shelf",
+      "curtains"
     ],
     "colors": [
       "pink",
-      "magenta",
-      "white",
       "fuchsia",
-      "pastel pink"
+      "purple"
     ],
-    "lighting": "bright, soft box, sparkling, dreamy, sunlight",
-    "theme": "barbiecore, dollhouse, girly, plastic, cute"
+    "lighting": "neon_lights, sparkle",
+    "theme": "barbie_(franchise), glitter, frills, kitsch"
   },
   "lora": {
     "lora_name": "Illustrious/Backgrounds/Barbie_b3dr00m-i.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "Barbie_b3dr00m-i"
+    "lora_triggers": "barbie bedroom"
   },
   "tags": [
-    "interior",
+    "barbie_(franchise)",
     "bedroom",
-    "barbie",
-    "pink",
-    "dollhouse",
-    "cozy",
-    "room"
+    "indoors",
+    "pink_theme",
+    "fuchsia",
+    "neon_lights",
+    "sparkle",
+    "sequins",
+    "gem",
+    "mirror",
+    "chandelier",
+    "frills",
+    "curtains",
+    "bed",
+    "pillow",
+    "handbag",
+    "high_heels",
+    "tiara",
+    "ribbon"
   ]
 }