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/femdom_held_down_illust.json

@@ -2,36 +2,31 @@
   "action_id": "femdom_held_down_illust",
   "action_name": "Femdom Held Down Illust",
   "action": {
-    "full_body": "dominant character straddling someone, pinning them to the surface, assertive posture, on top",
-    "head": "looking down at viewer (pov), dominance expression, chin tilted down",
-    "eyes": "narrowed, intense eye contact, looking down",
-    "arms": "extended downwards, locked elbows, exerting pressure",
-    "hands": "forcefully holding wrists against the surface, pinning hands, wrist grab",
-    "torso": "leaning forward slightly, arching back, looming over",
-    "pelvis": "straddling the subject's waist or chest, hips grounded",
-    "legs": "knees bent, kneeling on either side of the subject, thighs active",
-    "feet": "kneeling position, toes touching the ground or bed",
-    "additional": "pov, from below, power dynamic, submission, floor or bed background"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "girl_on_top, straddling, lying_on_back",
+    "head": "looking_down, looking_at_another",
+    "eyes": "forced_eye_contact",
+    "arms": "holding_another's_wrists, arms_above_head",
+    "hands": "grab, clenched_hands",
+    "torso": "on_back",
+    "pelvis": "straddled",
+    "legs": "spread_legs",
+    "feet": "barefoot",
+    "additional": "femdom, struggling, pinned, assertive_female"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Femdom_Held_Down_Illust.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Femdom_Held_Down_Illust"
+    "lora_weight": 0.8,
+    "lora_triggers": "fdom_held"
   },
   "tags": [
     "femdom",
-    "held down",
-    "pinning",
+    "assertive_female",
+    "rough_sex",
+    "girl_on_top",
     "straddling",
-    "on top",
-    "looking down",
-    "pov",
-    "from below",
-    "wrist grab",
-    "dominance"
+    "holding_another's_wrists",
+    "lying_on_back",
+    "pinned",
+    "struggling"
   ]
 }