Standalone module (no engine/index/filter-grammar deps) that normalizes
relative humantime (5h, -3m), absolute time-of-day (12:00, resolved to
today in UTC), and full date/RFC3339 literals (2024-01-15,
2024-01-15T12:00:00Z) into a single Timestamp, given a passed-in `now`
for testability. Adds humantime and chrono dependencies.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o
