feat(assets): async two-phase scanner and background seeder

- Rewrite scanner.py with two-phase scanning architecture (fast scan + enrich)
- Add AssetSeeder for non-blocking background startup scanning
- Implement pause/resume/stop/restart controls and disable/enable for --disable-assets-autoscan
- Add non-destructive asset pruning with is_missing flag
- Wire seeder into main.py and server.py lifecycle
- Skip hidden files/directories, populate mime_type, optional blake3 hashing
- Add comprehensive seeder tests

Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-019c9209-37af-757a-b6e4-af59b4267362

main.py

@@ -7,7 +7,7 @@ import folder_paths
 import time
 from comfy.cli_args import args, enables_dynamic_vram
 from app.logger import setup_logger
-from app.assets.scanner import seed_assets
+from app.assets.seeder import asset_seeder
 import itertools
 import utils.extra_config
 import logging
@@ -258,7 +258,11 @@ def prompt_worker(q, server_instance):
             for k in sensitive:
                 extra_data[k] = sensitive[k]
 
+            asset_seeder.pause()
+
             e.execute(item[2], prompt_id, extra_data, item[4])
+
+            asset_seeder.resume()
             need_gc = True
 
             remove_sensitive = lambda prompt: prompt[:5] + prompt[6:]
@@ -355,8 +359,10 @@ def setup_database():
         from app.database.db import init_db, dependencies_available
         if dependencies_available():
             init_db()
-            if not args.disable_assets_autoscan:
-                seed_assets(["models"], enable_logging=True)
+            if args.disable_assets_autoscan:
+                asset_seeder.disable()
+            elif asset_seeder.start(roots=("models", "input", "output"), prune_first=True, compute_hashes=True):
+                logging.info("Background asset scan initiated for models, input, output")
     except Exception as e:
         logging.error(f"Failed to initialize database. Please ensure you have installed the latest requirements. If the error persists, please report this as in future the database will be required: {e}")
 
@@ -440,5 +446,6 @@ if __name__ == "__main__":
         event_loop.run_until_complete(x)
     except KeyboardInterrupt:
         logging.info("\nStopped server")
-
-    cleanup_temp()
+    finally:
+        asset_seeder.shutdown()
+        cleanup_temp()