Calendar: add events (NE Hub calendar + iCloud) and a Podcast tab

- Add, edit and delete events; month/agenda views open them on tap
- NE Hub calendar stored on the server and published as a private ICS subscribe link
- iCloud CalDAV read/write with an app-specific password (encrypted at rest,
  only *.icloud.com contacted, event addresses checked against the calendar)
- Edits patch the existing entry so alarms/attendees survive; writes use If-Match / If-None-Match
- Time zone definitions (VTIMEZONE) generated so other apps read times correctly
- Podcast tab (PODCAST_URL) alongside Podcast Admin

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

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