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/guided_penetration_illustrious_v1_0.json

@@ -2,31 +2,30 @@
   "action_id": "guided_penetration_illustrious_v1_0",
   "action_name": "Guided Penetration Illustrious V1 0",
   "action": {
-    "full_body": "intimate sexual position, lying on back or missionary, lower body focus",
-    "head": "looking down, chin tucked, flushed face, heavy breathing",
-    "eyes": "focused on genitals, half-closed eyes, arousal",
-    "arms": "reaching down between legs",
-    "hands": "hand on penis, guiding penis, holding penis, fingers grasping shaft, touching tip",
-    "torso": "chest exposed, nipples visible, slight arch",
-    "pelvis": "exposed genitals, pussy, hips tilted up",
-    "legs": "spread legs, m legs, open legs, knees bent",
-    "feet": "relaxed or toes curled",
-    "additional": "penis, erection, insertion, just the tip, uncensored, sexual intercourse"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "guided_penetration",
+    "head": "looking_at_penis",
+    "eyes": "open_eyes",
+    "arms": "arms_extended",
+    "hands": "penis_grab",
+    "torso": "sex",
+    "pelvis": "vaginal",
+    "legs": "spread_legs",
+    "feet": "feet_out_of_frame",
+    "additional": "insertion"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/guided penetration_illustrious_V1.0.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "guided penetration_illustrious_V1.0"
+    "lora_weight": 1.1,
+    "lora_triggers": "guided penetration"
   },
   "tags": [
-    "guided penetration",
-    "hand on penis",
+    "guided_penetration",
+    "penis_grab",
+    "vaginal",
     "sex",
-    "insertion",
-    "guiding penis"
+    "1boy",
+    "1girl",
+    "penis",
+    "hands_on_penis"
   ]
 }