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/il_medieval_brothel_bedroom_r1.json

@@ -1,40 +1,42 @@
 {
   "scene_id": "il_medieval_brothel_bedroom_r1",
   "scene_name": "Il Medieval Brothel Bedroom R1",
-  "description": "A dimly lit, intimate medieval bedroom with rustic stone walls and luxurious red ornate fabrics, illuminated by warm candlelight and a fireplace.",
+  "description": "A dimly lit, rustic medieval bedroom featuring a large canopy bed, wooden interiors, and red drapery.",
   "scene": {
-    "background": "indoors, stone wall, wood flooring, arched window, fireplace, tapestry, medieval interior, wooden beams, night",
-    "foreground": "canopy bed, red bedding, messy sheets, velvet pillows, fur rug, ornate chair, goblet, washbasin",
+    "background": "indoors, wooden_wall, wooden_floor, window, night",
+    "foreground": "canopy_bed, carpet, candle",
     "furniture": [
-      "four-poster bed",
-      "vanity table",
-      "wooden trunk",
-      "dressing screen",
-      "candle stand"
+      "canopy_bed",
+      "carpet",
+      "curtains"
     ],
     "colors": [
-      "crimson",
       "brown",
-      "gold",
-      "amber",
-      "deep purple"
+      "red",
+      "orange"
     ],
-    "lighting": "candlelight, firelight, warm lighting, dim, volumetric lighting, atmospheric, low key",
-    "theme": "medieval, fantasy, romance, historical, rustic, intimate"
+    "lighting": "candlelight, dim_light",
+    "theme": "medieval, brothel, fantasy, red_theme"
   },
   "lora": {
     "lora_name": "Illustrious/Backgrounds/IL_Medieval_brothel_Bedroom_r1.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "IL_Medieval_brothel_Bedroom_r1"
+    "lora_triggers": "medieval_brothel, bedroom, canopy bed, wooden floor, wooden wall, candle, night, red curtains, carpet, window"
   },
   "tags": [
     "medieval",
-    "bedroom",
     "brothel",
-    "interior",
-    "fantasy",
-    "intricate",
-    "luxury",
-    "romantic atmosphere"
+    "bedroom",
+    "canopy_bed",
+    "wooden_floor",
+    "wooden_wall",
+    "candle",
+    "night",
+    "curtains",
+    "carpet",
+    "window",
+    "candlelight",
+    "dim_light",
+    "red_theme"
   ]
 }