Missing --until flag and today/yesterday keywords on every export subcommand

[DTTerastar]

Severity

major

Summary

The shipped binary only accepts --since, with absolute (YYYY-MM-DD) and relative (Nd/Nw/Nm/Ny) values. The contract requires:

• --until flag, inclusive, paired with --since
• today and yesterday keywords accepted by both flags

Without these, several documented prime/CONTRACT examples and any windowed query (e.g. "last week, excluding today") are impossible.

Reproduce

$ withings-export activity --until today
Error: unknown flag: --until

$ withings-export activity --since today
Error: invalid --since value: "today"

$ withings-export activity --since yesterday
Error: invalid --since value: "yesterday"

Help text:

--since string   Filter on or after date (e.g. 2026-01-01, 30d, 4w, 6m, 1y; default 30d)

no --until, no keyword mention.

Expected

Both flags accept today | yesterday | YYYY-MM-DD | Nd/Nw/Nm/Ny. --until is inclusive of the named day (CLI adds 24h internally per cmd/shared.go:parseUntilValue).

Already implemented on main (PR #8) but missing from v0.2.1 — see #14.

[DTTerastar]

Does not reproduce against HEAD b580683. Verified: activity --since today --until today, activity --since yesterday --until yesterday (returns row dated 2026-04-24), activity --since 2026-04-25 --until 2026-04-25 (inclusive — returns the April 25 row). Help text now lists today, yesterday, YYYY-MM-DD, or Nd/Nw/Nm/Ny and --until is shown. Fixed by PR #8. Closing.