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/futa_on_female_000051_1_.json

@@ -2,40 +2,28 @@
   "action_id": "futa_on_female_000051_1_",
   "action_name": "Futa On Female 000051 1 ",
   "action": {
-    "full_body": "intimate duo pose, futanari character positioning closely on top of female character, missionary or pressing variance",
-    "head": "flushed complexion, heavy breathing, looking at partner",
-    "eyes": "half-closed in pleasure, heart-shaped pupils, watery eyes",
-    "arms": "arms supporting weight on surface or embracing partner",
-    "hands": "grasping partner's shoulders or hips, fingers digging into skin",
-    "torso": "sweaty skin, leaning forward, chest contact",
-    "pelvis": "interlocked hips, penetrating action, engaged core",
-    "legs": "kneeling between partner's thighs, thighs touching",
-    "feet": "toes curled, arched feet",
-    "additional": "bodily fluids, motion lines, sweat, messy bed sheets"
-  },
-  "participants": {
-    "solo_focus": "false",
-    "orientation": "FF"
+    "full_body": "2girls, futa_with_female, sex",
+    "head": "looking_at_viewer, blush",
+    "eyes": "open_eyes",
+    "arms": "braided_arms, grabbing_hips",
+    "hands": "on_hips",
+    "torso": "breasts, nipples",
+    "pelvis": "futanari, penis, vaginal, pussy",
+    "legs": "spread_legs, straddling",
+    "feet": "barefoot",
+    "additional": "duo, bodily_fluids"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Futa_on_Female-000051(1).safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "Futa_on_Female-000051(1)"
+    "lora_triggers": "futa with female"
   },
   "tags": [
+    "futa_with_female",
     "futanari",
-    "futa_on_female",
-    "1girl",
-    "1futanari",
+    "2girls",
     "vaginal",
     "sex",
-    "penis",
-    "erection",
-    "pussy",
-    "cum",
-    "sweat",
-    "blush",
-    "duo",
-    "nsfw"
+    "breasts"
   ]
 }