feat(settings): add settings page with server, watchdog and notification config

- Add new Settings view with form controls for server, watchdog and notification settings
- Implement API endpoints for getting and saving settings
- Add settings route and sidebar navigation item
- Update button styles to include text color variable
- Change default app target to local development address

src/styles/common.css

@@ -445,6 +445,7 @@
     font-family: 'SF Pro Text', 'SF Pro Icons', 'Helvetica Neue', Helvetica, Arial, sans-serif;
     padding: 8px 15px;
     background: var(--surface-light);
+    color: var(--text-color);
     border: none;
     border-radius: 8px;
     cursor: pointer;