test(core): route-tuning note 'reset at ...Z' parsed in local time — normalization test fails outside UTC #29

Problem

packages/core/test/config/normalization.test.ts → "notes survive normalization and reach the tuner as match and text" fails on unmodified main when the process timezone is not UTC.

Reproduced 2026-10-17 (Bun 1.4.2):

• TZ=America/Chicago bun run script/test.ts test/config/normalization.test.ts → 42 pass, 1 fail
• TZ=UTC bun run script/test.ts test/config/normalization.test.ts → 43 pass, 0 fail

The note anthropic/claude-opus-5: promo credits, reset at 2026-01-04T00:00:00Z should produce a skip adjustment with until = Date.parse("2026-01-04T00:00:00Z") (1767484800000). Under America/Chicago the tuner returns until = 1767506400000 — exactly +6h, i.e. the Z-suffixed timestamp is being interpreted as local midnight instead of UTC.

Impact

If the parsing path is shared with production (not just the test), a user outside UTC gets route-tuning notes that expire hours early/late. Either way the test suite is red for every non-UTC contributor.

Suggested fix

Parse the note timestamp as UTC when it carries a Z (or normalize through Date.parse on the full ISO string rather than reconstructing a local date), and/or pin the tuner's parsing to UTC. Add a non-UTC regression run for this test.

Found by the issue sweep while verifying #14; unrelated to that change (fails identically on clean main).