fix(email): restore two-arg luxon fromObject in matchTeamIntro timeslots

[detail-app]

Detail bug report: View on Detail

Bug

The match-team intro email (src/email/templates/matchTeamIntro.ts) silently dropped its "Suggested Meeting Times (all students available)" block for any matched team whose students actually supplied weekly availability data, falling back to the generic "Mentors: Send a When2meet" prompt instead.

Root cause: localIntervalToUtc built each luxon DateTime with DateTime.fromObject({ …, zone: tz }) — placing zone inside the values object. Under the installed runtime luxon@3.7.2 this throws InvalidUnitError: Invalid unit zone (zone is not a valid unit there; luxon 3.x takes the zone via a second options argument). A broad try/catch in findCommonTimeslots swallowed the throw and returned {}, which getList collapsed to undefined, so the template's {{#if commonTimeslots}} branch never rendered.

This slipped through typecheck because @types/luxon was pinned to a stale ^1.26.5 whose fromObject signature accepts the extra zone key, masking the runtime/types mismatch — and through testing because the code had no test coverage at all.

Fix

• Restored the two-argument DateTime.fromObject(values, { zone }) form for both the start and end conversions in localIntervalToUtc — the form the original feature commit used before the regression.
• Bumped @types/luxon from ^1.26.5 to ^3.7.5 so the type definitions match the ^3.7.2 runtime. This both lets the correct two-arg form typecheck and turns the buggy single-arg form into a compile error (TS2345: 'zone' does not exist in type 'DateObjectUnits'), preventing the identical regression from reoccurring. The whole repo still typechecks cleanly against the upgraded types.
• Left the findCommonTimeslots try/catch in place; the throw it was masking is gone, and a regression test now asserts no console.warn is emitted for valid data.
• Added an offline regression test (matchTeamIntro.test.ts, stubbed Prisma) covering the core regression, cross-timezone UTC conversion, the swallowed-error guard, the legitimate-empty fallback, and both template branches.

Testing

• Unit tests, typecheck (npx tsc --skipLibCheck --noEmit), and the existing unrelated offline test (syncAlumniInteractions.test.ts) all pass. (ESLint is broken environment-wide — eslint 7's parser is incompatible with the installed TS 5.x — and is not a usable signal here.)
• New offline regression test (npx tsx src/email/templates/matchTeamIntro.test.ts) verifies: overlapping same-timezone availability yields a populated commonTimeslots; cross-timezone overlap (NY 9–11am / LA 6–8am, both 14:00–16:00 UTC) renders the window in each student's own timezone; no "finding common timeslots" warning is emitted for valid data; missing timeManagementPlan legitimately yields undefined; and the actual matchTeamIntro.md Handlebars block renders the "Suggested Meeting Times" block (not When2meet) when data is supplied, and the When2meet fallback (not the timeslot block) when it isn't.
• Verified end-to-end against a live Postgres DB: installed and started postgresql-16, created a test database, applied the schema via prisma db push, seeded a matched project with two accepted students in distinct timezones and overlapping availability plus an accepted mentor on a matchComplete event, and ran the real dispatch path (getEmailGenerators() → generator.getList() → generator.template() with the app's Handlebars helpers registered). The rendered email body contained the "Suggested Meeting Times" header with both timezone-labeled windows and no When2meet fallback; after clearing the students' plans, it rendered the When2meet fallback instead. Seed data was cleaned up afterward.
• Confirmed the regression-guard: temporarily reverting to the buggy fromObject({ …, zone }) form produces TS2345 compile errors under the upgraded types, so the build now blocks reintroduction.

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