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/doggydoublefingering.json

@@ -2,32 +2,32 @@
   "action_id": "doggydoublefingering",
   "action_name": "Doggydoublefingering",
   "action": {
-    "full_body": "all fours, doggy style, kneeling, presenting rear, from behind",
-    "head": "looking back, looking at viewer, blushing face",
-    "eyes": "half-closed eyes, expressionless or aroused",
-    "arms": "reaching back between legs, reaching towards crotch",
-    "hands": "fingering, double fingering, both hands used, spreading vaginal lips, manipulating genitals",
-    "torso": "arched back, curvature of spine",
-    "pelvis": "hips raised, presenting pussy, exposed gluteal crease",
-    "legs": "knees bent on ground, thighs spread",
-    "feet": "toes curled, relaxing instep",
-    "additional": "pussy juice, focus on buttocks, focus on genitals"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "Three females arranged side-by-side in a row, all facing away from viewer or towards viewer depending on angle, engaged in group sexual activity",
+    "head": "various expressions, blushing, sweating, looking back or down",
+    "eyes": "open or closed in pleasure",
+    "arms": "varied, gripping sheets or supporting body",
+    "hands": "resting on surface or gripping",
+    "torso": "leaning forward, breasts visible if from front",
+    "pelvis": "hips raised, bent over",
+    "legs": "kneeling on all fours",
+    "feet": "resting on bed or ground",
+    "additional": "center female receiving vaginal penetration from behind (doggystyle), two distinct side females being fingered simultaneously, male figure or disembodied hands performing the fingering"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/DoggyDoubleFingering.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "DoggyDoubleFingering"
+    "lora_triggers": "doggydoublefingerfront, from front, 3girls, multiple girls, fingering, sex from behind, doggystyle"
   },
   "tags": [
-    "masturbation",
-    "solo",
-    "ass focus",
-    "pussy",
-    "kneeling",
-    "NSFW"
+    "3girls",
+    "group_sex",
+    "doggystyle",
+    "fingering",
+    "all_fours",
+    "sex_from_behind",
+    "vaginal",
+    "hetero",
+    "harem",
+    "male_fingering"
   ]
 }