fix: add withTimezone to all wxyc_schema timestamp columns

[jakebromberg]

Summary

• All 14 timestamp() columns in wxyc_schema tables were missing { withTimezone: true }, making them ambiguous during DST transitions. Auth tables (public schema) already used withTimezone. This aligns the two.
• Adds a unit test (tests/unit/database/schema.timestamps.test.ts) that reads the schema source and asserts every timestamp() call includes withTimezone: true, preventing future regressions.
• No migration generated — that will be a separate step.

Affected tables

shift_covers, artists, library, flowsheet, genres, reviews, shows, specialty_shows, album_metadata, artist_metadata

Test plan

• Unit test fails before fix (14 columns detected)
• Unit test passes after fix
• Verify existing integration tests still pass in CI
• Generate and review migration separately before deploying

Closes #39

Made with Cursor

Note: This fix is consolidated in #199 (coordinated schema migration batch). Consider closing in favor of #199.

[AyBruno]

This is good for safety I suppose, but any inserts/updates we perform on timestamp fields already default to UTC and shouldn't technically require this.