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/threesome_sex_and_rimminganilingus.json

@@ -2,35 +2,33 @@
   "action_id": "threesome_sex_and_rimminganilingus",
   "action_name": "Threesome Sex And Rimminganilingus",
   "action": {
-    "full_body": "threesome, group sex, three characters interacting, one character receiving anilingus while interacting with a third",
-    "head": "face buried in buttocks, tongue extended, expressions of pleasure, looking back",
-    "eyes": "eyes closed, rolled back, ahegao, intense focus",
-    "arms": "holding hips, grabbing sheets, supporting body weight, reaching between legs",
-    "hands": "spreading buttocks, gripping waist, fingering, touching",
-    "torso": "bent over, arched back, leaning forward",
-    "pelvis": "lifted hips, presenting anus, gluteal cleft exposed",
-    "legs": "kneeling, all fours, legs spread wide, straddling",
-    "feet": "barefoot, toes curled, plantar flexion",
-    "additional": "rimming, anilingus, saliva, Ass focus, explicit, wet"
-  },
-  "participants": {
-    "solo_focus": "false",
-    "orientation": "MFF"
+    "full_body": "ffm_threesome, group_sex, standing_sex, sex_from_behind, from_side",
+    "head": "open_mouth, tongue, blush, ahegao, heavy_breathing",
+    "eyes": "heart-shaped_pupils",
+    "arms": "hands_on_another's_hips",
+    "hands": "grabbing_hips",
+    "torso": "large_breasts, nipples, wet_skin",
+    "pelvis": "nude, pubic_hair",
+    "legs": "standing",
+    "feet": "barefoot",
+    "additional": "anilingus, implied_anilingus, motion_lines, twitching"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Threesome_sex_and_rimminganilingus.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "Threesome_sex_and_rimminganilingus"
+    "lora_triggers": "ffm_sex_and_anilingus"
   },
   "tags": [
-    "threesome",
-    "group sex",
-    "rimming",
+    "ffm_threesome",
+    "group_sex",
+    "standing_sex",
+    "sex_from_behind",
     "anilingus",
-    "ass licking",
-    "spreading",
-    "all fours",
-    "doggystyle",
-    "explicit"
+    "nude",
+    "open_mouth",
+    "tongue",
+    "blush",
+    "motion_lines",
+    "from_side"
   ]
 }