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/actions/girls_lineup_il_1144149.json

@@ -2,35 +2,28 @@
   "action_id": "girls_lineup_il_1144149",
   "action_name": "Girls Lineup Il 1144149",
   "action": {
-    "full_body": "standing, police lineup, mugshot, full body shot",
-    "head": "looking at viewer, neutral expression, facing forward",
-    "eyes": "open eyes, staring",
-    "arms": "arms at sides, arms behind back",
-    "hands": "hands behind back",
-    "torso": "facing forward, upright posture",
-    "pelvis": "facing forward",
-    "legs": "standing straight, feet shoulder width apart",
-    "feet": "flat on ground",
-    "additional": "height chart, wall markings, measurement lines, police station background, indoor, simple background"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "multiple girls standing in a row",
+    "head": "facing viewer",
+    "eyes": "looking at viewer",
+    "arms": "arms at sides",
+    "hands": "hands at sides",
+    "torso": "standing",
+    "pelvis": "facing viewer",
+    "legs": "standing",
+    "feet": "standing",
+    "additional": "simple background"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/girls_lineup_IL_1144149.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "girls_lineup_IL_1144149"
+    "lora_triggers": "lineup"
   },
   "tags": [
-    "police lineup",
-    "mugshot",
-    "height chart",
+    "lineup",
+    "multiple_girls",
     "standing",
-    "criminal",
-    "arrest",
-    "prison",
-    "law enforcement",
-    "measurement"
+    "facing_viewer",
+    "looking_at_viewer",
+    "simple_background"
   ]
 }