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/upside_down_missionary_illustriousxl_lora_nochekaiser.json

@@ -2,35 +2,34 @@
   "action_id": "upside_down_missionary_illustriousxl_lora_nochekaiser",
   "action_name": "Upside Down Missionary Illustriousxl Lora Nochekaiser",
   "action": {
-    "full_body": "duo focus, sexual position, lying on back, partner on top facing feet, reverse missionary, bodies aligned in opposite directions",
-    "head": "resting on surface, head back, facing upwards",
-    "eyes": "rolled back or looking at partner's back, half-closed",
-    "arms": "resting on bed or holding partner's thighs, arms at sides",
-    "hands": "clutching sheets or gripping partner",
-    "torso": "chest upwards, back flat on surface",
-    "pelvis": "hops raised, engaged in intercourse",
-    "legs": "legs spread wide, knees bent, legs up, m-legs or wrapped around partner's waist",
-    "feet": "toes curled, soles visible if legs raised",
-    "additional": "on bed, intimate angle, detailed anatomy"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "lying, on_back, missionary, upside-down, spread_legs",
+    "head": "upside-down, head_down",
+    "eyes": "open_eyes, looking_at_viewer",
+    "arms": "arms_at_sides, arms_up",
+    "hands": "grabbing_sheet, sheet_grab",
+    "torso": "chest_up, on_back, navel, collarbone",
+    "pelvis": "legs_spread, hips_up",
+    "legs": "spread_legs, knees_bent, legs_up",
+    "feet": "feet_up",
+    "additional": "blush, open_mouth, torso_grab, partner_hand_on_torso"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/upside-down-missionary-illustriousxl-lora-nochekaiser.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "upside-down-missionary-illustriousxl-lora-nochekaiser"
+    "lora_triggers": "upside-down missionary, upside-down, missionary, on_back, spread_legs, torso_grab, sheet_grab"
   },
   "tags": [
-    "upside-down missionary",
-    "reverse missionary",
-    "lying on back",
-    "legs up",
-    "spread legs",
-    "duo",
-    "sex",
-    "vaginal",
-    "m-legs"
+    "upside-down",
+    "missionary",
+    "lying",
+    "on_back",
+    "spread_legs",
+    "sheet_grab",
+    "torso_grab",
+    "blush",
+    "open_mouth",
+    "navel",
+    "collarbone",
+    "from_above"
   ]
 }