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/wedding_venue.json

@@ -1,37 +1,43 @@
 {
   "scene_id": "wedding_venue",
   "scene_name": "Wedding Venue",
-  "description": "A grand and romantic indoor wedding venue adorned with white floral arrangements, an elegant aisle runner, and soft, ethereal lighting illuminating the altar.",
+  "description": "A romantic outdoor wedding reception area set in a lush garden, featuring decorated tables and floral arches perfectly prepared for a celebration.",
   "scene": {
-    "background": "indoors, church, stained glass, window, altar, arch, scenery, architecture",
-    "foreground": "aisle, carpet, flower petals, white flower, rose, no humans",
+    "background": "outdoors, scenery, garden, nature, floral_arch, flower, tree, shrub",
+    "foreground": "table, tablecloth, bouquet, chair, dishware, bloom",
     "furniture": [
-      "pew",
+      "table",
       "chair",
-      "chandelier",
-      "podium",
-      "vase"
+      "floral_arch"
     ],
     "colors": [
       "white",
-      "gold",
-      "pastel pink",
-      "cream"
+      "green",
+      "pink",
+      "pastel_colors"
     ],
-    "lighting": "sunlight, volumetric lighting, bright, soft lighting, bloom",
-    "theme": "wedding, romance, ceremony, elegance"
+    "lighting": "day, sunlight, soft_lighting, natural_light",
+    "theme": "wedding, party, romance, celebration, formal"
   },
   "lora": {
     "lora_name": "Illustrious/Backgrounds/Wedding_Venue.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Wedding_Venue"
+    "lora_weight": 0.7,
+    "lora_triggers": "w3dd1ng"
   },
   "tags": [
+    "w3dd1ng",
+    "outdoors",
     "wedding",
-    "church",
-    "interior",
-    "romantic",
-    "flowers",
-    "ceremony"
+    "table",
+    "bouquet",
+    "tablecloth",
+    "floral_arch",
+    "flower",
+    "party",
+    "scenery",
+    "garden",
+    "chair",
+    "nature",
+    "day"
   ]
 }