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/sex_machine.json

@@ -2,33 +2,40 @@
   "action_id": "sex_machine",
   "action_name": "Sex Machine",
   "action": {
-    "full_body": "lying on back, mating press, legs lifted high and spread wide, body compacted, hips elevated",
-    "head": "head thrown back into pillow, mouth wide open, tongue out, expression of intense pleasure",
-    "eyes": "eyes rolled back, heart-shaped pupils, eyelids heavy",
-    "arms": "reaching forward or gripping bedsheets tightly above head, strained muscles",
-    "hands": "clenched fists, fingers digging into fabric",
-    "torso": "arched back, chest heaving, glistening with sweat",
-    "pelvis": "tilted upward, exposed, engaged in action",
-    "legs": "legs up, knees bent heavily towards shoulders, m-legs, wide stance",
-    "feet": "toes curled, pointing upward or resting on partner's shoulders",
-    "additional": "messy bed sheets, motion lines, steam, liquid details, high contrast"
-  },
-  "participants": {
-    "solo_focus": "true",
-    "orientation": "MF"
+    "full_body": "sitting, spread_legs, restrained",
+    "head": "gagged, screaming, wince, head_back",
+    "eyes": "tears, forced_orgasm",
+    "arms": "bound_wrists, shackles, mechanical_arms",
+    "hands": "bound",
+    "torso": "arched_back, trembling",
+    "pelvis": "object_insertion, sex_machine, dildo",
+    "legs": "spread_legs, bound_ankles",
+    "feet": "shackles",
+    "additional": "stationary_restraints, motion_lines"
   },
   "lora": {
     "lora_name": "Illustrious/Poses/Sex_Machine.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "Sex_Machine"
+    "lora_weight": 0.7,
+    "lora_triggers": "Sex Machine, stationary restraints"
   },
   "tags": [
-    "mating press",
-    "legs up",
-    "ahegao",
-    "sweaty",
-    "messy bed",
-    "intense",
-    "nsfw"
+    "sex_machine",
+    "stationary_restraints",
+    "sitting",
+    "spread_legs",
+    "bound_wrists",
+    "bound_ankles",
+    "shackles",
+    "gagged",
+    "arched_back",
+    "forced_orgasm",
+    "screaming",
+    "wince",
+    "tears",
+    "trembling",
+    "object_insertion",
+    "dildo",
+    "mechanical_arms",
+    "motion_lines"
   ]
 }