Fix HBO primetime release time to use ET-local conversion

[x-n2o]

Summary

While double-checking Euphoria's published times, I noticed the calendar event for S03E06 ("Stand Still and See") was landing about 23 hours too early.

What went wrong

US_PRIMETIME was a literal UTC string ("02:00:00Z") stamped on the TMDb air_date. TMDb's air_date is the local US broadcast date, but HBO airs in late-evening ET — so the resulting UTC moment fell on the previous day in ET:

Episode	TMDb air_date	Old startsAt	In ET	Actual HBO broadcast
Euphoria S03E06	2026-05-17	2026-05-17T02:00:00Z	Sat May 16, 10pm EDT	Sun May 17, 9pm EDT (2026-05-18T01:00:00Z)

The PT/ET midnight strategies already do DST-aware local→UTC conversion via localMidnightToUtc. US_PRIMETIME did not.

Fix

• Treat US_PRIMETIME as 21:00 America/New_York and reuse the DST-aware local-to-UTC conversion (generalized localMidnightToUtc → localTimeToUtc).
• Restructure strategies so each entry is either { localTime, timezone } or { utc }.
• Drop Euphoria's redundant releaseTime: "02:00:00Z" override so it picks up the corrected HBO strategy.
• Update README to document the new local-time, DST-aware strategies.

Test plan

• pnpm test — 30 passed (added two HBO regression tests covering EDT and EST air dates)
• pnpm run typecheck
• pnpm run build
• Re-subscribe to /api/cal/euphoria.ics and confirm S03E06 now shows Mon May 18 02:00 BST (i.e., Sun May 17 9pm EDT) in the calendar client

[Copilot]

Pull request overview

Fixes HBO primetime release time conversion which was previously stamping a literal UTC string and resulting in events being ~23 hours too early. The fix generalizes the existing DST-aware local→UTC helper to handle arbitrary local times (not just midnight) and restructures strategies as a discriminated union of { localTime, timezone } or { utc }.

Changes:

• Generalized localMidnightToUtc to localTimeToUtc, accepting a local time component with DST-aware offset resolution.
• Restructured strategies into a tagged union and routed all resolution through a single resolveStrategyDateTime helper; US_PRIMETIME now means 21:00 America/New_York.
• Removed redundant releaseTime override on Euphoria, updated README, and added EDT/EST regression tests.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/release.ts	Generalize local-time conversion, refactor strategies to tagged union, simplify resolveDateTime.
src/shows.ts	Drop Euphoria's now-redundant releaseTime override.
tests/release.test.ts	Add HBO primetime regression tests for both EDT and EST air dates.
README.md	Document new local-time, DST-aware strategy format.

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