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/extreme_sex_v1_0_illustriousxl.json

@@ -2,36 +2,33 @@
   "action_id": "extreme_sex_v1_0_illustriousxl",
   "action_name": "Extreme Sex V1 0 Illustriousxl",
   "action": {
-    "full_body": "lying on back, mating press, legs lifted high, dynamic angle, foreshortening",
-    "head": "head leaning back, heavy blush, sweat, mouth open, tongue out, intense expression",
-    "eyes": "rolling eyes, heart-shaped pupils, eyelashes",
-    "arms": "arms reaching forward, grabbing sheets, or holding own legs",
-    "hands": "clenched hands, grabbing",
-    "torso": "arched back, chest exposed, sweat on skin",
-    "pelvis": "hips lifted, pelvis tilted upwards",
-    "legs": "legs spread, m-legs, legs folded towards torso, knees bent",
-    "feet": "feet in air, toes curled, plantar view",
-    "additional": "motion lines, shaking, bodily fluids, bed sheet, pillow"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "sitting, engaging in sexual activity, intense body language",
+    "head": "tilted back, expression of ecstasy",
+    "eyes": "rolling_eyes, loss of focus, cross-eyed (ahegao)",
+    "arms": "clinging or holding partner",
+    "hands": "grasping details",
+    "torso": "heaving, covered in sweat",
+    "pelvis": "engaged in action",
+    "legs": "wrapped around or spread",
+    "feet": "toes curled",
+    "additional": "drooling, saliva_trail, flushing, messy_hair"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/extreme-sex-v1.0-illustriousxl.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "extreme-sex-v1.0-illustriousxl"
+    "lora_triggers": "extreme sex"
   },
   "tags": [
-    "mating press",
-    "lying on back",
-    "legs up",
-    "open mouth",
-    "blush",
-    "sweat",
-    "m-legs",
-    "intense",
+    "rolling_eyes",
     "ahegao",
-    "explicit"
+    "drooling",
+    "sweat",
+    "open_mouth",
+    "tongue_out",
+    "messy_hair",
+    "heavy_breathing",
+    "blush",
+    "mind_break",
+    "sex"
   ]
 }