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/pov_cellphone_screen_stevechopz.json

@@ -2,36 +2,30 @@
   "action_id": "pov_cellphone_screen_stevechopz",
   "action_name": "Pov Cellphone Screen Stevechopz",
   "action": {
-    "full_body": "first-person perspective view of a hand holding a smartphone in the foreground, framing a subject on the screen",
-    "head": "subject's face visible on the digital display, looking into the lens",
-    "eyes": "direct eye contact from the subject on the screen",
-    "arms": "viewer's arm extending into frame holding the device",
-    "hands": "viewer's hand gripping a black smartphone, one hand holding phone",
-    "torso": "subject on screen cropped from chest up or full body depending on zoom",
+    "full_body": "pov, first-person_view",
+    "head": "looking_at_phone",
+    "eyes": "looking_at_viewer",
+    "arms": "pov_hands, holding_phone",
+    "hands": "holding_phone",
+    "torso": "upper_body",
     "pelvis": "n/a",
     "legs": "n/a",
     "feet": "n/a",
-    "additional": "phone layout, camera ui, recording stats, blurred background behind the phone, depth of field"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "additional": "smartphone, viewfinder, taking_picture, recording"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/POV_Cellphone_Screen_SteveChopz.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "POV_Cellphone_Screen_SteveChopz"
+    "lora_triggers": "ChoPS, pov hands, cellphone, holding cellphone, phone screen, cellphone picture, 5 fingers"
   },
   "tags": [
     "pov",
-    "holding phone",
+    "pov_hands",
+    "holding_phone",
     "smartphone",
-    "phone screen",
-    "display",
-    "recording",
-    "camera interface",
-    "depth of field",
-    "technology",
-    "social media"
+    "viewfinder",
+    "taking_picture",
+    "looking_at_phone",
+    "1girl"
   ]
 }