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/scenes/m4dscienc3_il.json

@@ -1,37 +1,53 @@
 {
   "scene_id": "m4dscienc3_il",
   "scene_name": "M4Dscienc3 Il",
-  "description": "A dark, cluttered laboratory filled with chaotic experiments, glowing chemical flasks, and sparking electrical equipment.",
+  "description": "A freaky, funky laboratory full of strange inventions, bubbling chemicals, and ominous machines with a Saturday morning cartoon vibe.",
   "scene": {
-    "background": "indoors, laboratory, science fiction, mess, cluttered, wires, pipes, servers, electronics on wall, monitors, vapor",
-    "foreground": "flask, beaker, test tube, glowing liquid, bubbling, smoke, sparks, electricity, tesla coil, paperwork, glass shards",
+    "background": "dungeon, stone_wall, brick_wall, indoors, scenery, dark",
+    "foreground": "flask, beaker, test_tube, glowing_liquid, green_liquid, purple_liquid, smoke, bubbles, electricity",
     "furniture": [
-      "workbench",
-      "metal shelving",
-      "rusty table",
-      "control console"
+      "machine",
+      "table",
+      "desk",
+      "shelf",
+      "monitor",
+      "cable",
+      "wire"
     ],
     "colors": [
-      "neon green",
-      "electric blue",
-      "dark grey",
-      "rust orange"
+      "green",
+      "purple",
+      "black",
+      "grey"
     ],
-    "lighting": "dimly lit, cinematic lighting, volumetric lighting, glow from chemicals, bloom",
-    "theme": "mad science, cyberpunk, ominous, eccentric, hazard"
+    "lighting": "dim_lighting, glowing, ominous",
+    "theme": "science_fiction, horror_(theme), cartoon"
   },
   "lora": {
     "lora_name": "Illustrious/Backgrounds/M4DSCIENC3-IL.safetensors",
     "lora_weight": 1.0,
-    "lora_triggers": "M4DSCIENC3-IL"
+    "lora_triggers": "M4DSCIENC3, laboratory, dungeon"
   },
   "tags": [
-    "masterpiece",
-    "best quality",
-    "highres",
-    "detailed background",
-    "illustration",
-    "concept art",
-    "scifi"
+    "laboratory",
+    "dungeon",
+    "science_fiction",
+    "horror_(theme)",
+    "machine",
+    "flask",
+    "beaker",
+    "test_tube",
+    "glowing_liquid",
+    "green_liquid",
+    "purple_liquid",
+    "smoke",
+    "cable",
+    "wire",
+    "monitor",
+    "electricity",
+    "dark",
+    "indoors",
+    "no_humans",
+    "scenery"
   ]
 }