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/woman_on_top_pov_il_2.json

@@ -2,34 +2,33 @@
   "action_id": "woman_on_top_pov_il_2",
   "action_name": "Woman On Top Pov Il 2",
   "action": {
-    "full_body": "pov, straddling, woman on top, cowgirl position, sitting on viewer",
-    "head": "looking down, looking at viewer, face close to camera",
-    "eyes": "eye contact, seductive gaze",
-    "arms": "hands on viewer's chest, bracing arms",
-    "hands": "palms flattening, touching chest",
-    "torso": "leaning forward, breasts hanging, stomach view",
-    "pelvis": "crotch contact, hips active",
-    "legs": "knees bent, spread legs, thighs framing view",
-    "feet": "out of frame",
-    "additional": "from below, male pov, lying on back (viewer), intimate angle"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "girl_on_top, straddling, leaning_forward, sitting_on_person",
+    "head": "looking_down, looking_at_viewer",
+    "eyes": "looking_at_viewer",
+    "arms": "leaning_on_person",
+    "hands": "hands_on_own_hips",
+    "torso": "hanging_breasts, leaning_forward",
+    "pelvis": "straddling",
+    "legs": "kneeling, spread_legs",
+    "feet": "out_of_frame",
+    "additional": "pov, from_below, low_angle, foreshortening"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Woman On Top POV-IL-2.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Woman On Top POV-IL-2"
+    "lora_weight": 0.8,
+    "lora_triggers": "woman on top, fetop, from below"
   },
   "tags": [
-    "pov",
-    "woman on top",
-    "cowgirl position",
-    "looking down",
+    "girl_on_top",
     "straddling",
-    "hands on chest",
-    "from below",
-    "intimate"
+    "leaning_forward",
+    "looking_down",
+    "from_below",
+    "pov",
+    "hanging_breasts",
+    "long_hair",
+    "looking_at_viewer",
+    "sitting_on_person",
+    "leaning_on_person"
   ]
 }