Fix jobs date filter timezone normalization

[suguanYang]

Summary

• normalize jobs list start_time and end_time query filters into naive UTC before DB comparisons
• make recent_days and result URL expiry calculations use the same naive UTC convention
• add a contract regression test for ISO UTC Z date filters on /v1/jobs/page

Tests

• uv run pytest apps/api/tests/contract/test_job_read_contract.py::test_should_list_jobs_when_date_filters_use_iso_utc_timezone
• uv run pytest apps/api/tests/contract/test_job_read_contract.py
• make lint
• make typecheck

Fixes #37