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/straddling_kiss_illustriousxl_lora_nochekaiser.json

@@ -2,34 +2,32 @@
   "action_id": "straddling_kiss_illustriousxl_lora_nochekaiser",
   "action_name": "Straddling Kiss Illustriousxl Lora Nochekaiser",
   "action": {
-    "full_body": "two subjects, intimate couple pose, one subject sitting on the other's lap facing them, straddling position",
-    "head": "faces close together, kissing, lips joined, side profile view, tilted heads",
-    "eyes": "closed eyes, affectionate expression",
-    "arms": "arms wrapping around neck, arms embracing waist, holding each other close",
-    "hands": "cupping face, hands on waist, hands grasping shoulders, fingers in hair",
-    "torso": "chests pressed together, bodies leaning into each other",
-    "pelvis": "sitting on lap, pelvis close contact, weight supported by partner",
-    "legs": "legs wrapped around partner's waist, knees bent, thighs straddling hips",
-    "feet": "feet dangling or hooked behind partner's back",
-    "additional": "romantic atmosphere, blushing, floating hearts, intimate interaction"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "girl on top, upright straddle, straddling partner while sitting on them",
+    "head": "kissing, tilted head, blushing",
+    "eyes": "closed eyes",
+    "arms": "arms around partner's neck, embracing",
+    "hands": "resting on shoulders or holding face",
+    "torso": "upright posture, chest pressing against partner",
+    "pelvis": "sitting on partner's waist/hips",
+    "legs": "straddling partner's torso, knees bent",
+    "feet": "tucked or resting on the surface",
+    "additional": "intimate atmosphere, on bed"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/straddling-kiss-illustriousxl-lora-nochekaiser.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "straddling-kiss-illustriousxl-lora-nochekaiser"
+    "lora_triggers": "straddling kiss"
   },
   "tags": [
     "straddling",
     "kiss",
-    "lap sitting",
+    "girl_on_top",
+    "upright_straddle",
+    "sitting_on_person",
     "couple",
-    "intimate",
-    "legs wrapped around",
-    "romance",
-    "embrace"
+    "on_bed",
+    "closed_eyes",
+    "blush",
+    "arms_around_neck"
   ]
 }