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/ponyplay_illustrious.json

@@ -2,36 +2,34 @@
   "action_id": "ponyplay_illustrious",
   "action_name": "Ponyplay Illustrious",
   "action": {
-    "full_body": "on all fours, quadrupedal pose, mimicking a horse",
-    "head": "wearing bridle, bit gag in mouth, looking forward",
-    "eyes": "wide, submissive, focused",
-    "arms": "straightened, supporting weight, vertical",
-    "hands": "wearing hoof gloves or resting on fists",
-    "torso": "arched back, wearing leather harness",
-    "pelvis": "hips raised, faxt tail attached to rear",
-    "legs": "knees on ground, thighs perpendicular to floor",
-    "feet": "wearing hoof boots or pointing backwards",
-    "additional": "reins attached to bridle, fetish gear, animalistic posture"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "on_all_fours, crawling",
+    "head": "bit_gag, horse_ears",
+    "eyes": "looking_at_viewer",
+    "arms": "arms_behind_back, bound_arms",
+    "hands": "restricted",
+    "torso": "rope_harness, bondage_gear",
+    "pelvis": "horse_tail",
+    "legs": "kneeling",
+    "feet": "barefoot",
+    "additional": "acting like an animal, pet play scenario"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Ponyplay_Illustrious.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Ponyplay_Illustrious"
+    "lora_weight": 0.7,
+    "lora_triggers": "ponyplay, pet play, slave"
   },
   "tags": [
-    "ponyplay",
-    "human pony",
-    "on all fours",
+    "pony_play",
+    "pet_play",
+    "bit_gag",
+    "horse_ears",
+    "horse_tail",
+    "harness",
+    "bondage",
     "bdsm",
-    "leather harness",
-    "bridle",
-    "bit gag",
-    "hooves",
-    "animal play",
-    "fetish"
+    "on_all_fours",
+    "fake_ears",
+    "animal_ears",
+    "leather"
   ]
 }