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/bathingtogether.json

@@ -2,33 +2,30 @@
   "action_id": "bathingtogether",
   "action_name": "Bathingtogether",
   "action": {
-    "full_body": "two characters sharing a bathtub, sitting close together in water",
-    "head": "wet hair, flushed cheeks, relaxed expressions, looking at each other",
-    "eyes": "gentle gaze, half-closed",
-    "arms": "resting on the tub rim, washing each other, or embracing",
-    "hands": "holding soap, sponge, or touching skin",
-    "torso": "wet skin, water droplets, partially submerged, steam rising",
-    "pelvis": "submerged in soapy water",
-    "legs": "knees bent, submerged, intertwined",
-    "feet": "underwater",
-    "additional": "bathroom tiles, steam clouds, soap bubbles, rubber duck, faucet"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "bathing, sitting, partially_submerged",
+    "head": "looking_at_viewer, facing_viewer",
+    "eyes": "eye_contact",
+    "arms": "arms_resting",
+    "hands": "resting",
+    "torso": "bare_shoulders",
+    "pelvis": "submerged",
+    "legs": "knees_up, submerged",
+    "feet": "no_shoes",
+    "additional": "bathtub, steam, water, bubbles, wet"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/bathingtogether.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "bathingtogether"
+    "lora_triggers": "bathing together"
   },
   "tags": [
     "bathing",
-    "couple",
+    "bathtub",
+    "partially_submerged",
+    "pov",
+    "looking_at_viewer",
     "wet",
     "steam",
-    "bathtub",
-    "shared bath",
-    "soap bubbles"
+    "bare_shoulders"
   ]
 }