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/lap_pov_illustriousxl_lora_nochekaiser.json

@@ -2,33 +2,32 @@
   "action_id": "lap_pov_illustriousxl_lora_nochekaiser",
   "action_name": "Lap Pov Illustriousxl Lora Nochekaiser",
   "action": {
-    "full_body": "pov, sitting on lap, straddling, shot from above, close-up, intimate distance",
-    "head": "looking up, chin tilted up, face close to camera",
-    "eyes": "eye contact, looking at viewer, intense gaze",
-    "arms": "arms around neck, embracing viewer, or hands resting on viewer's chest",
-    "hands": "touching viewer, resting on shoulders",
-    "torso": "upper body close to viewer, leaning slightly back",
-    "pelvis": "sitting on viewer's thighs, weight settled",
-    "legs": "knees bent, thighs visible, straddling viewer's legs, spread legs",
-    "feet": "out of frame or dangling",
-    "additional": "viewer's legs visible beneath, depth of field, own hands (pov)"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "lap_pillow, pov",
+    "head": "looking_down, blush, smile",
+    "eyes": "eye_contact",
+    "arms": "arms_not_visible",
+    "hands": "hands_not_visible",
+    "torso": "from_below, navel",
+    "pelvis": "thighs",
+    "legs": "sitting",
+    "feet": "feet_out_of_frame",
+    "additional": "ceiling"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/lap-pov-illustriousxl-lora-nochekaiser.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "lap-pov-illustriousxl-lora-nochekaiser"
+    "lora_triggers": "lap pov, lap pillow, from below, ceiling, looking down, pov"
   },
   "tags": [
+    "lap_pillow",
     "pov",
-    "sitting on lap",
-    "straddling",
-    "looking up",
-    "from above",
-    "intricate details",
-    "highly detailed"
+    "from_below",
+    "looking_down",
+    "lap_pov",
+    "eye_contact",
+    "ceiling",
+    "thighs",
+    "navel",
+    "lying_on_lap"
   ]
 }