refactor: separate podcasts from downloads — own route + nav item

- /podcasts — new page with PodcastPlayer (headphones icon)
- /downloads — old media page renamed (download icon)
- /media — kept for backward compat (same as downloads)
- Nav: Reader → Podcasts → Downloads → Brain

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

services/brain/storage/a66d0767-a59e-4ede-878d-f74441e42830/original_upload/test-insurance.pdf

@@ -1,19 +0,0 @@
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-BT /F1 18 Tf 72 700 Td (State Farm Insurance Policy) Tj ET
-BT /F1 12 Tf 72 670 Td (Policy Number: SF-2024-881234) Tj ET
-BT /F1 12 Tf 72 650 Td (Policyholder: Yusuf Suleman) Tj ET
-BT /F1 12 Tf 72 630 Td (Deductible: 500 dollars) Tj ET
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