Same-titled episodes from different podcasts collapse into one queue entry #356

Problem. The queue identifies episodes by title alone (src/store/index.ts:216-228,264-268,464-468). Two episodes with the same title from different podcasts, such as "Trailer", collapse into one queue entry, and playing one removes the other. A jsdom probe confirmed it; src/store/index.test.ts:423 pins the current behavior.

Acceptance. Both episodes stay in the queue and play independently. Fixed through stable episode identity (see the GUID identity issue), with a migration test for existing queues.

Found by the PodNotes codebase audit.