feat(spi): add native fetcher SPI interface for background content fetching

- Add NativeNotificationContentFetcher interface for host app implementations
- Add FetchContext class to pass fetch parameters (trigger, scheduledTime, fetchTime)
- Add SchedulingPolicy class for retry backoff configuration
- Add TypeScript definitions for content fetcher SPI in src/definitions.ts
- Export SPI types from src/index.ts

This enables host apps to provide their own content fetching implementation
for background workers, following the Integration Point Refactor (PR2).

src/definitions.ts

@@ -8,6 +8,12 @@
  * @version 2.0.0
  */
 
+// Import SPI types from content-fetcher.ts
+import type {
+  SchedulingPolicy,
+  JsNotificationContentFetcher
+} from './types/content-fetcher';
+
 export interface NotificationResponse {
   id: string;
   title: string;
@@ -442,6 +448,43 @@ export interface DailyNotificationPlugin {
    * Update an existing daily reminder
    */
   updateDailyReminder(reminderId: string, options: DailyReminderOptions): Promise<void>;
+
+  // Integration Point Refactor (PR1): SPI Registration Methods
+  
+  /**
+   * Set JavaScript content fetcher for foreground operations
+   * 
+   * NOTE: This is a stub in PR1. Full implementation coming in PR3.
+   * JS fetchers are ONLY used for foreground/manual refresh.
+   * Background workers must use native fetcher.
+   * 
+   * @param fetcher JavaScript fetcher implementation
+   */
+  setJsContentFetcher(fetcher: JsNotificationContentFetcher): void;
+
+  /**
+   * Enable or disable native fetcher
+   * 
+   * Native fetcher is required for background workers. If disabled,
+   * background fetches will fail gracefully.
+   * 
+   * @param enable Whether to enable native fetcher
+   * @returns Promise with enabled and registered status
+   */
+  enableNativeFetcher(enable: boolean): Promise<{
+    enabled: boolean;
+    registered: boolean;
+  }>;
+
+  /**
+   * Set scheduling policy configuration
+   * 
+   * Updates the scheduling policy used by the plugin for retry backoff,
+   * prefetch timing, deduplication, and cache TTL.
+   * 
+   * @param policy Scheduling policy configuration
+   */
+  setPolicy(policy: SchedulingPolicy): Promise<void>;
 }
 
 // Phase 1: TimeSafari Endorser.ch API Interfaces