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/neba.json

@@ -2,31 +2,29 @@
   "action_id": "neba",
   "action_name": "Neba",
   "action": {
-    "full_body": "character posing while stretching a viscous, sticky substance between body parts",
-    "head": "tilted slightly forward or back, focused on the substance",
-    "eyes": "focused gaze, watching the strands stretch",
-    "arms": "extended outwards or pulled apart to create tension in the liquid",
-    "hands": "fingers spread, pulling sticky material apart with visible strands connecting them",
-    "torso": "posture adjusts to accommodate the stretching motion",
-    "pelvis": "neutral or slightly shifted weight",
-    "legs": "standing or sitting planted firmly",
-    "feet": "neutral placement",
-    "additional": "thick, stringy strands (neba neba) connecting hands to other surfaces or body parts, implies viscosity"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "character covered in viscous slime substance, wet and shiny skin",
+    "head": "slime dripping from face, flushed expression",
+    "eyes": "wide open eyes",
+    "arms": "arms coated in sticky liquid",
+    "hands": "slimy hands",
+    "torso": "slime running down body",
+    "pelvis": "wet with slime",
+    "legs": "legs covered in slippery slime",
+    "feet": "standing in slime puddle",
+    "additional": "sticky strands, messy texture, high viscosity"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/neba.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "neba"
+    "lora_triggers": "black slime, pink slime, white slime, green slime, yellow slime, transparent slime, mud slime, slime (substance)"
   },
   "tags": [
-    "neba neba",
+    "slime_(substance)",
     "sticky",
-    "stretching",
-    "viscous",
-    "slime"
+    "wet",
+    "shiny_skin",
+    "dripping",
+    "blush",
+    "open_mouth"
   ]
 }