feat(anki): add media timing review before card creation

- Add draggable timing previews with audio playback and exact media ranges
- Support cancellation choices, including deleting existing cards

src/types/subtitle.ts

@@ -243,6 +243,8 @@ export interface SubtitleMiningContext {
   startTime: number;
   endTime: number;
   capturedAtMs?: number;
+  /** Explicit generator padding. Confirmed timing-review ranges set this to zero. */
+  mediaPaddingSeconds?: number;
 }
 
 export interface SubtitleHoverTokenPayload {