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/pose_nipple_licking_handjob_3.json

@@ -2,20 +2,16 @@
   "action_id": "pose_nipple_licking_handjob_3",
   "action_name": "Pose Nipple Licking Handjob 3",
   "action": {
-    "full_body": "duo, intimate pose, character leaning forward over partner, sexual activity, close proximity",
-    "head": "face near chest, licking, tongue out, sucking nipple, mouth open",
-    "eyes": "half-closed eyes, focused expression, lustful gaze",
-    "arms": "reaching down towards crotch, engaging contact",
-    "hands": "handjob, gripping penis, stroking, manual stimulation, skin tight",
-    "torso": "leaning forward, chest pressed or close, exposed nipples",
-    "pelvis": "erection, penis, genital exposure",
-    "legs": "kneeling, straddling, sitting",
-    "feet": "out of frame or curled",
-    "additional": "saliva, arousal, sweat"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "duo, sexual_activity",
+    "head": "tongue_out",
+    "eyes": "looking_at_partner",
+    "arms": "reaching",
+    "hands": "handjob, holding_penis",
+    "torso": "licking_nipple",
+    "pelvis": "penis, testicles, erection",
+    "legs": "standing",
+    "feet": "standing",
+    "additional": "1boy, 1girl, hetero"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/pose_nipple_licking_handjob_3.safetensors",
@@ -23,13 +19,16 @@
     "lora_triggers": "pose_nipple_licking_handjob_3"
   },
   "tags": [
-    "nipple_licking",
+    "1boy",
+    "1girl",
+    "hetero",
+    "sexual_activity",
     "handjob",
-    "duo",
-    "sexual_act",
+    "licking_nipple",
+    "tongue_out",
     "penis",
-    "licking",
-    "sucking",
-    "tongue"
+    "testicles",
+    "erection",
+    "duo"
   ]
 }