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/cumblastfacial.json

@@ -0,0 +1,32 @@
+{
+  "action_id": "cumblastfacial",
+  "action_name": "Cumblastfacial",
+  "action": {
+    "full_body": "solo, bukkake",
+    "head": "facial, head_tilt, looking_up",
+    "eyes": "cum_in_eye",
+    "arms": "arms_down",
+    "hands": "hands_down",
+    "torso": "cum_on_upper_body",
+    "pelvis": "standing",
+    "legs": "standing",
+    "feet": "standing",
+    "additional": "projectile_cum, excessive_cum, ejaculation"
+  },
+  "lora": {
+    "lora_name": "Illustrious/Poses/cumblastfacial.safetensors",
+    "lora_weight": 1.0,
+    "lora_triggers": "xcbfacialx"
+  },
+  "tags": [
+    "facial",
+    "projectile_cum",
+    "bukkake",
+    "excessive_cum",
+    "ejaculation",
+    "head_tilt",
+    "looking_up",
+    "cum_in_eye",
+    "cum_on_hair"
+  ]
+}