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/pov_sitting_on_lap_illustrious_000005.json

@@ -2,34 +2,33 @@
   "action_id": "pov_sitting_on_lap_illustrious_000005",
   "action_name": "Pov Sitting On Lap Illustrious 000005",
   "action": {
-    "full_body": "pov, sitting on lap, straddling, close physical proximity",
-    "head": "facing viewer, slightly looking down",
-    "eyes": "intense eye contact, looking at viewer",
-    "arms": "shoulders raise, arms wrapped around viewer's neck or resting on viewer's chest",
-    "hands": "interlocked behind viewer's head or touching viewer's shoulders",
-    "torso": "leaning forward, upper body close to camera",
-    "pelvis": "seated directly on viewer",
-    "legs": "legs apart, straddling, knees bent outward, thighs visible at bottom of frame",
-    "feet": "out of frame or dangling",
-    "additional": "intimate atmosphere, foreshortening, first-person perspective"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "pov, sitting_on_lap, straddling",
+    "head": "looking_at_viewer, from_above",
+    "eyes": "looking_at_viewer",
+    "arms": "reaching_towards_viewer, arms_around_neck",
+    "hands": "reaching_towards_viewer",
+    "torso": "leaning_forward",
+    "pelvis": "sitting, squatting, straddling",
+    "legs": "legs_apart, straddling, kneeling",
+    "feet": "kneeling",
+    "additional": "1girl, 1boy, sexual_innuendo"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Pov_Sitting_on_Lap_Illustrious-000005.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "Pov_Sitting_on_Lap_Illustrious-000005"
+    "lora_triggers": "pov sitting on lap"
   },
   "tags": [
     "pov",
-    "sitting on lap",
+    "sitting_on_lap",
     "straddling",
-    "arms around neck",
-    "looking at viewer",
-    "intimate",
-    "legs apart",
-    "close-up"
+    "looking_at_viewer",
+    "reaching_towards_viewer",
+    "squatting",
+    "1girl",
+    "1boy",
+    "from_above",
+    "from_below",
+    "facing_away"
   ]
 }