feat(fetcher): add configureNativeFetcher cross-platform API

Add configureNativeFetcher() plugin method to enable TypeScript configuration
of native fetchers with API credentials. This provides a cross-platform
mechanism for passing configuration from JavaScript to native code without
relying on platform-specific storage.

- Add configure() method to NativeNotificationContentFetcher interface
  (optional, defaults to no-op for fetchers that don't need config)
- Add configureNativeFetcher plugin method in DailyNotificationPlugin
- Add TypeScript definitions and comprehensive JSDoc
- Create NATIVE_FETCHER_CONFIGURATION.md documentation
- Update TestNativeFetcher to use real API endpoint (10.0.2.2:3000)
- Update DemoNativeFetcher Javadoc explaining configure() is optional
- Add configureNativeFetcher() call to demo app's configurePlugin()

Enables host apps to configure native fetchers from TypeScript, keeping
the interface consistent across Android, iOS, and web platforms.

android/plugin/src/main/java/com/timesafari/dailynotification/NativeNotificationContentFetcher.java

@@ -82,5 +82,62 @@ public interface NativeNotificationContentFetcher {
      */
     @NonNull
     CompletableFuture<List<NotificationContent>> fetchContent(@NonNull FetchContext context);
+    
+    /**
+     * Optional: Configure the native fetcher with API credentials and settings
+     * 
+     * <p>This method is called by the plugin when {@code configureNativeFetcher} is invoked
+     * from TypeScript. It provides a cross-platform mechanism for passing configuration
+     * from the JavaScript layer to native code without using platform-specific storage
+     * mechanisms.</p>
+     * 
+     * <p><b>When to implement:</b></p>
+     * <ul>
+     *   <li>Your fetcher needs API credentials (URL, authentication tokens, etc.)</li>
+     *   <li>Configuration should come from TypeScript/JavaScript code (e.g., from app config)</li>
+     *   <li>You want to avoid hardcoding credentials in native code</li>
+     * </ul>
+     * 
+     * <p><b>When to skip (use default no-op):</b></p>
+     * <ul>
+     *   <li>Your fetcher gets credentials from platform-specific storage (SharedPreferences, Keychain, etc.)</li>
+     *   <li>Your fetcher has hardcoded test credentials</li>
+     *   <li>Configuration is handled internally and doesn't need external input</li>
+     * </ul>
+     * 
+     * <p><b>Thread Safety:</b> This method may be called from any thread. Implementations
+     * must be thread-safe if storing configuration in instance variables.</p>
+     * 
+     * <p><b>Implementation Pattern:</b></p>
+     * <pre>{@code
+     * private volatile String apiBaseUrl;
+     * private volatile String activeDid;
+     * private volatile String jwtSecret;
+     * 
+     * @Override
+     * public void configure(String apiBaseUrl, String activeDid, String jwtSecret) {
+     *     this.apiBaseUrl = apiBaseUrl;
+     *     this.activeDid = activeDid;
+     *     this.jwtSecret = jwtSecret;
+     *     Log.i(TAG, "Fetcher configured with API: " + apiBaseUrl);
+     * }
+     * }</pre>
+     * 
+     * @param apiBaseUrl Base URL for API server. Examples:
+     *                   - Android emulator: "http://10.0.2.2:3000" (maps to host localhost:3000)
+     *                   - iOS simulator: "http://localhost:3000"
+     *                   - Production: "https://api.timesafari.com"
+     * @param activeDid Active DID (Decentralized Identifier) for authentication.
+     *                  Used as the JWT issuer/subject. Format: "did:ethr:0x..."
+     * @param jwtSecret JWT secret key for signing authentication tokens.
+     *                  Keep this secure - consider using secure storage for production.
+     * 
+     * @see DailyNotificationPlugin#configureNativeFetcher(PluginCall)
+     */
+    default void configure(String apiBaseUrl, String activeDid, String jwtSecret) {
+        // Default no-op implementation - fetchers that need config can override
+        // This allows fetchers that don't need TypeScript-provided configuration
+        // to ignore this method without implementing an empty body.
+    }
 }