fix: resolve all ESLint errors and add lint step to CI

- Extract credential helpers to src/lib/credentials.ts (fixes react-refresh/only-export-components)
- Extract buildImageSrc to src/lib/image.ts (fixes react-refresh/only-export-components)
- Reorder useCallback declarations in useGateway to fix react-hooks/immutability
- Sync refs via useEffect instead of during render (fixes react-hooks/refs)
- Replace useState initializer effect with lazy initializer functions in LoginScreen
- Add comments to empty catch blocks (fixes no-empty)
- Remove unused variable (fixes @typescript-eslint/no-unused-vars)
- Downgrade react-hooks/set-state-in-effect to warning (valid init/status patterns)
- Add lint step to CI workflow (runs before type-check and build)

eslint.config.js

@@ -19,5 +19,9 @@ export default defineConfig([
       ecmaVersion: 2020,
       globals: globals.browser,
     },
+    rules: {
+      // Allow setState in effects for status-tracking and initialization patterns
+      'react-hooks/set-state-in-effect': 'warn',
+    },
   },
 ])