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/danglinglegs.json

@@ -2,32 +2,30 @@
   "action_id": "danglinglegs",
   "action_name": "Danglinglegs",
   "action": {
-    "full_body": "holding waist, dangling legs, size difference",
-    "head": "facing forward or looking down",
-    "eyes": "relaxed gaze",
-    "arms": "resting on lap or gripping the edge of the seat",
-    "hands": "placed on thighs or holding on",
-    "torso": "upright sitting posture",
-    "pelvis": "seated on edge",
-    "legs": "dangling in the air, knees bent at edge, feet not touching the floor",
-    "feet": "relaxed, hanging loose",
-    "additional": "sitting on ledge, sitting on desk, high stool"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "suspended_congress, lifting_person, standing_sex",
+    "head": "clenched_teeth, head_back",
+    "eyes": "eyes_closed",
+    "arms": "arms_around_neck",
+    "hands": "hands_on_shoulders",
+    "torso": "body_lifted",
+    "pelvis": "hips_held",
+    "legs": "legs_apart, feet_off_ground",
+    "feet": "toes_up, barefoot",
+    "additional": "size_difference, larger_male, sex_from_behind"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/danglinglegs.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "danglinglegs"
+    "lora_triggers": "dangling legs, lifted by penis, suspended on penis"
   },
   "tags": [
-    "dangling legs",
-    "sitting",
-    "feet off ground",
-    "from below",
-    "ledge",
-    "high place"
+    "suspended_congress",
+    "lifting_person",
+    "standing_sex",
+    "sex_from_behind",
+    "size_difference",
+    "toes_up",
+    "barefoot",
+    "clenched_teeth"
   ]
 }