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/pov_sex.json

@@ -2,38 +2,33 @@
   "action_id": "pov_sex",
   "action_name": "Pov Sex",
   "action": {
-    "full_body": "pov, first-person view, partner lying on back, intimate proximity, from above",
-    "head": "head resting on pillow, chin tilted up, flushed face, messy hair, heavy breathing expression",
-    "eyes": "looking at viewer, intense eye contact, half-closed eyes, bedroom eyes, pupils dilated",
-    "arms": "reaching up towards camera, embracing viewer or gripping bed sheets",
-    "hands": "fingers curled, holding viewer's shoulders or clutching sheets",
-    "torso": "supine, lying on bed, chest exposed, slightly arched back",
-    "pelvis": "legs spread wide, hips elevated, engaging with viewer",
-    "legs": "wrapped around viewer's waist or knees bent and spread, legs up",
-    "feet": "toes curled, typically out of focus or frame",
-    "additional": "sweat drop, disheveled bed sheets, viewer's hands visible on partner's body, cinematic lighting"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "missionary, lying, on_back",
+    "head": "looking_at_viewer, blush",
+    "eyes": "open_eyes, looking_at_viewer",
+    "arms": "holding_legs, arms_up",
+    "hands": "grabbing_own_thighs",
+    "torso": "breasts, nipples",
+    "pelvis": "vaginal, penis, insertion",
+    "legs": "legs_together, legs_up",
+    "feet": "toes_curled",
+    "additional": "pov, sex, hetero, 1boy, 1girl"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/POV_SEX.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "POV_SEX"
+    "lora_triggers": "POV_SEX_V1"
   },
   "tags": [
     "pov",
-    "looking at viewer",
-    "missionary",
-    "lying on back",
-    "legs wrapped",
     "sex",
-    "intimate",
-    "sweat",
-    "blush",
-    "bed",
-    "messy sheets",
-    "from above"
+    "missionary",
+    "vaginal",
+    "lying",
+    "on_back",
+    "legs_together",
+    "holding_legs",
+    "penis",
+    "hetero",
+    "rating:explicit"
   ]
 }