Preserve release-local timestamps and timezones; increase cache TTL

[x-n2o]

Motivation

• Emit calendar events using release-local timestamps and preserve human-readable IANA time zones instead of forcing UTC so calendar clients display correct local times.
• Ensure the ICS generator includes timezone metadata when available and make platform strategies carry timezone information.
• Increase edge cache lifetime for generated feeds.

Description

• Change release strategies to floating times and add a strategyTimeZone mapping with human-readable IANA zones, and introduce validators/normalizers: isoDatePattern, timePattern, isoDateTimePattern, combineDateAndTime, and normalizeIsoDateTime.
• Add resolveReleaseTimeZone and return a timeZone on ShowEpisode when a platform strategy applies, and include timeZone in generated ICS events by setting the event timezone property in generateICS.
• Update types by adding timeZone?: string to ShowEpisode and adjust getShowEpisodes to populate timeZone and startsAt via resolveReleaseTimeZone/resolveDateTime.
• Increase Cache-Control header from max-age=1800 to max-age=3600.
• Update tests to reflect new behaviors and validations and adapt expected timestamp formats (no forced Z for midnight and platform strategies return floating midnight plus timezone info).

Testing

• Ran unit tests with vitest, including release.test.ts, tmdb.test.ts, and router.test.ts, and all tests passed.
• Exercised generateICS changes via router tests to confirm Content-Type, Cache-Control, and event SUMMARY remained correct under the new timezone handling.

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Codex Task