Add settings page, PIN manager, and auto-config

- New settings page at /settings (localhost-only) accessible via tray icon
- PIN manager with 6-digit codes, 5-min TTL, single-use
- API token uses secrets.token_urlsafe(32) for 256-bit entropy
- Config auto-creates config.yaml on first run with detected local IP
- Default PIN and token generated randomly on first startup
- Added pin_ttl setting (default 300s)
- Updated build_exe.py for onefile exe with settings assets bundled
- Added start.bat and start.sh for easy development startup

client/app.js

@@ -515,8 +515,7 @@
 				return;
 			}
 
-			SETTINGS_STATUS.textContent =
-				strings.settings_saved || "Settings saved";
+			SETTINGS_STATUS.textContent = strings.settings_saved || "Settings saved";
 			currentApiToken = token;
 		} catch (err) {
 			SETTINGS_STATUS.textContent =