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/arm_grab_missionary_ill_10.json

@@ -2,35 +2,37 @@
   "action_id": "arm_grab_missionary_ill_10",
   "action_name": "Arm Grab Missionary Ill 10",
   "action": {
-    "full_body": "lying on back, missionary position, submissive posture",
-    "head": "head tilted back, blushing, heavy breathing",
-    "eyes": "looking at viewer, half-closed eyes, rolling eyes",
-    "arms": "arms raised above head, arms grabbed, wrists held, armpits exposed",
-    "hands": "hands pinned, helpless",
-    "torso": "arched back, chest exposed",
-    "pelvis": "exposed crotch",
-    "legs": "spread legs, knees bent upwards, m-legs",
-    "feet": "toes curled",
-    "additional": "on bed, bed sheet, pov, submission, restraint"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "missionary, lying, on_back, sex, vaginal",
+    "head": "expressive face, open mouth, one_eye_closed, blushing",
+    "eyes": "looking_at_viewer (optional), dilated_pupils",
+    "arms": "arms_up, pinned, restrained, grabbed_wrists",
+    "hands": "interlocked_fingers, holding_hands",
+    "torso": "breasts, nipples, medium_breasts",
+    "pelvis": "legs_spread, lifted_pelvis",
+    "legs": "spread_legs, legs_up, knees_up, straddling (if applicable)",
+    "feet": "barefoot (implied)",
+    "additional": "faceless_male, male_focus, motion_lines, sweat"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/arm_grab_missionary_ill-10.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "arm_grab_missionary_ill-10"
+    "lora_triggers": "arm_grab_missionary"
   },
   "tags": [
-    "arm grab",
     "missionary",
-    "lying on back",
-    "arms above head",
-    "wrists held",
-    "legs spread",
-    "armpits",
-    "submission",
-    "pov"
+    "spread_legs",
+    "interlocked_fingers",
+    "holding_hands",
+    "arms_up",
+    "pinned",
+    "lying",
+    "on_back",
+    "sex",
+    "vaginal",
+    "faceless_male",
+    "one_eye_closed",
+    "open_mouth",
+    "breasts",
+    "nipples"
   ]
 }