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/multiple_views_sex.json

@@ -2,34 +2,28 @@
   "action_id": "multiple_views_sex",
   "action_name": "Multiple Views Sex",
   "action": {
-    "full_body": "multiple views, split view, character sheet, three-view drawing, front view, side view, back view",
-    "head": "neutral expression, looking forward, head visible from multiple angles",
-    "eyes": "open, direct gaze (in front view)",
-    "arms": "arms at sides, A-pose or T-pose, relaxed",
-    "hands": "open hands, relaxed",
-    "torso": "standing straight, visible from front, side, and back",
-    "pelvis": "facing forward (front view), facing side (side view)",
-    "legs": "standing straight, legs slightly apart",
-    "feet": "flat on floor",
-    "additional": "simple background, white background, concept art style, anatomy reference"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "multiple_views, sex, doggystyle, all_fours",
+    "head": "looking_back",
+    "eyes": "open_eyes",
+    "arms": "on_ground",
+    "hands": "on_ground",
+    "torso": "arched_back, bent_over",
+    "pelvis": "lifted",
+    "legs": "kneeling",
+    "feet": "toes_pointing",
+    "additional": "split_screen"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Multiple_views_sex.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Multiple_views_sex"
+    "lora_weight": 0.8,
+    "lora_triggers": "multiple_views"
   },
   "tags": [
-    "multiple views",
-    "character turnaround",
-    "reference sheet",
-    "split view",
-    "from front",
-    "from side",
-    "from back",
-    "model sheet"
+    "multiple_views",
+    "sex",
+    "doggystyle",
+    "from_side",
+    "from_behind",
+    "split_screen"
   ]
 }