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_blowjob__titjob__handjob_illustrious_000005.json

@@ -0,0 +1,37 @@
+{
+  "action_id": "pov_blowjob__titjob__handjob_illustrious_000005",
+  "action_name": "Pov Blowjob Titjob Handjob Illustrious 000005",
+  "action": {
+    "full_body": "pov, kneeling, fellatio, paizuri, handjob",
+    "head": "looking_at_viewer, deepthroat",
+    "eyes": "looking_at_viewer",
+    "arms": "head_grab",
+    "hands": "handjob",
+    "torso": "breasts, cleavage, underboob",
+    "pelvis": "kneeling",
+    "legs": "kneeling",
+    "feet": "barefoot",
+    "additional": "pov B+T+H, one handed, two handed, cum_in_mouth"
+  },
+  "lora": {
+    "lora_name": "Illustrious/Poses/Pov_Blowjob__Titjob__Handjob_Illustrious-000005.safetensors",
+    "lora_weight": 1.0,
+    "lora_triggers": "pov, 1girl, 1boy, fellatio, paizuri, handjob, pov B+T+H"
+  },
+  "tags": [
+    "pov",
+    "looking_at_viewer",
+    "fellatio",
+    "paizuri",
+    "handjob",
+    "deepthroat",
+    "head_grab",
+    "cum_in_mouth",
+    "cleavage",
+    "underboob",
+    "kneeling",
+    "from_above",
+    "from_below",
+    "dutch_angle"
+  ]
+}