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/impossiblefit.json

@@ -2,34 +2,32 @@
   "action_id": "impossiblefit",
   "action_name": "Impossiblefit",
   "action": {
-    "full_body": "character standing, struggling to close or pull up extremely tight clothing that is too small for their body type",
-    "head": "tilted down looking at waist, face flushed or straining",
-    "eyes": "focused downwards on the clothing gap",
-    "arms": "bent at elbows, exerting force",
-    "hands": "gripping waistband, pulling zipper tab, or pinching fabric edges together",
-    "torso": "stomach sucked in, torso arched slightly backward or scrunched forward",
-    "pelvis": "hips emphasized, flesh compressed by tight fabric, potential muffin top",
-    "legs": "standing close together, knees sometimes bent for leverage",
-    "feet": "planted on ground, or hopping on one foot",
-    "additional": "clothing gap, open zipper, bursting buttons, skin indentation, clothes too small"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "kneeling on ground, facing partner",
+    "head": "looking down, looking at penis",
+    "eyes": "wide open, expression of awe or fear, blushing",
+    "arms": "reaching forward or hands protecting body",
+    "hands": "tentative touch or handjob",
+    "torso": "leaning slightly back or forward in anticipation",
+    "pelvis": "kneeling",
+    "legs": "kneeling, spread or together",
+    "feet": "tucked behind",
+    "additional": "extreme size difference, sweat drops, open mouth"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/impossiblefit.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "impossiblefit"
+    "lora_triggers": "impossible fit"
   },
   "tags": [
-    "tight clothing",
-    "clothes too small",
-    "struggling",
-    "clothing gap",
-    "muffin top",
-    "zipper",
-    "embarrassed",
-    "curvy"
+    "size_difference",
+    "huge_penis",
+    "imminent_penetration",
+    "penis_awe",
+    "looking_at_penis",
+    "blush",
+    "sweat",
+    "scared",
+    "open_mouth",
+    "penis_on_stomach"
   ]
 }