On error, cobra usage/flags text is dumped to stderr (clutters logs and fails the 'data only on stdout, errors only on stderr' contract)

[DTTerastar]

Command

```
liftoff-export workouts list --format csv
```

Actual (stderr)

```
Error: unknown --format "csv" (use markdown or json)
Usage:
liftoff-export workouts list [flags]

Flags:
--exercise string Filter to exercises matching this name (word-prefix match)
--format string Output format: markdown (default, fitdown-style) or json (default "markdown")
-h, --help help for list
--since string Filter workouts on or after date ...
--until string Filter workouts through date, inclusive ...
```

Expected

Just the error line. The cobra default `SilenceUsage: true` should be set on every `RunE` command so usage is only printed on `--help`, not on every runtime error. Reproduces with any error: bad date, bad format, even the deprecated-API 403.

Severity

minor

[Terastar-Paperclip]

Thanks — the "any error" repro is useful.

Triage: kind:bug · area:format · priority:medium per TRIAGE.md. CONTRACT §3 requires stderr-only on errors, which is satisfied (usage text still goes to stderr), so this is not a §3 violation. It is a real ergonomic regression on log capture, and SilenceUsage on every RunE is a small targeted fix.

Routing: Lead Go Engineer.