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/reversemilking_illu_dwnsty.json

@@ -2,33 +2,34 @@
   "action_id": "reversemilking_illu_dwnsty",
   "action_name": "Reversemilking Illu Dwnsty",
   "action": {
-    "full_body": "character straddling partner or object while facing away, reverse cowgirl stance, kneeling position",
-    "head": "turned back looking over shoulder or facing forward away from view",
-    "eyes": "looking back at viewer or closed in pleasure",
-    "arms": "arms supporting weight on the surface or reaching back to hold partner",
-    "hands": "hands pressing down on bed or holding own thighs",
-    "torso": "back arched, leaning forward slightly to accentuate buttocks",
-    "pelvis": "hips lowered, buttocks spread, engaging in straddling motion",
-    "legs": "knees bent, legs spread wide, straddling",
-    "feet": "toes dragging or feet flat on bed",
-    "additional": "emphasis on dorsal view and buttocks, motion lines often implied"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "kneeling, between_legs",
+    "head": "head_tilt, looking_at_viewer",
+    "eyes": "detailed_eyes",
+    "arms": "arms_reaching",
+    "hands": "handjob, reverse_grip, penis_grab",
+    "torso": "leaning_forward",
+    "pelvis": "kneeling",
+    "legs": "kneeling",
+    "feet": "feet_tucked",
+    "additional": "motion_lines, hand_up, sweat"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/ReverseMilking_Illu_Dwnsty.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "ReverseMilking_Illu_Dwnsty"
+    "lora_triggers": "reverse-grip milking, testicles, penis, 1boy, between legs"
   },
   "tags": [
-    "reverse cowgirl",
-    "straddling",
-    "from behind",
-    "ass focus",
-    "looking back",
-    "back arched",
-    "kneeling"
+    "handjob",
+    "reverse_grip",
+    "kneeling",
+    "penis",
+    "testicles",
+    "between_legs",
+    "clothed_female_nude_male",
+    "from_behind",
+    "penis_grab",
+    "motion_lines",
+    "looking_at_viewer",
+    "solo_focus"
   ]
 }