Subcommand flag is --json (boolean) instead of --format (markdown|json|csv) #22

Severity

major

Summary

Every export subcommand exposes a boolean --json flag rather than the contract's --format markdown|json|csv. As a result:

• Users can't request markdown at all (it's not the default and there's no flag for it).
• The documented behaviour in prime / README — --format json, --format csv — does not work on the shipped binary.
• Cross-CLI shell scripts that pass --format json to every quantcli tool fail here.

Reproduce

$ withings-export activity --help
Flags:
  --json           Output as JSON instead of CSV
  --since string   ...
$ withings-export activity --format json
Error: unknown flag: --format
$ withings-export activity --format markdown
Error: unknown flag: --format

Same on sleep, workouts, measurements, intraday.

Expected

Per the contract and the source's own validateFormat helper in cmd/shared.go:

--format markdown   (default)
--format json       (pretty-printed JSON array; epoch seconds for timestamps)
--format csv        (spreadsheet-friendly columnar output)

Implemented on main (PR #7) — missing from v0.2.1 (see #14). If --json needs to live on for backwards compat, alias it to --format json and mark it deprecated.