auth refresh subcommand: usage block dumped on success and bare 'auth' invocation

[DTTerastar]

Severity

cosmetic

Summary

Bare `withings-export auth` with no subcommand exits 0 and prints the help block to stdout (Cobra default). For a contract-driven CLI where stdout is data, this is a small stdout-pollution risk for shell-script consumers that key on `auth status` succeeding while another wrapper accidentally drops the `status`.

Reproduce

HEAD `b58068351a2edeb90f0d26b9098f04e85db225ee`.

$ /tmp/qa-bin/withings-export auth; echo \"EXIT=\$?\"
Authentication commands

Usage:
  withings-export auth [command]
...
EXIT=0

`auth bogus` correctly errors with EXIT=1, so the issue is specific to the bare-parent case.

Expected

• `auth` with no subcommand should exit non-zero (or, at minimum, print the help block to stderr instead of stdout). The same applies to the top-level `withings-export` (no subcommand) which also exits 0. Setting `Args: cobra.NoArgs` plus a `RunE` that returns `cmd.Help()` and a non-zero exit aligns with the contract's "exit non-zero only on auth or network failure" rule for missing-arg vs success.

Severity rationale

Cosmetic: nothing breaks today, but the empty-line of stdout on a misuse can corrupt JSON pipelines.

[DTTerastar]

@claude PR in a fix for this

[claude]

Claude finished @DTTerastar's task in 3m 51s —— View job • claude/issue-28-20260426-0007 • Create PR ➔

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Fix: exit non-zero and print help to stderr for bare invocations

• Analyze issue context
• Read codebase structure (auth command, root command)
• Implement fix for auth command — bare auth now exits 1 and prints help to stderr
• Implement fix for root command — bare withings-export now exits 1 and prints help to stderr
• Commit and push changes

What changed:

Both authCmd (cmd/auth.go) and rootCmd (cmd/root.go) now have a RunE that:

1. Redirects cmd.SetOut to stderr so the help block goes to stderr (not stdout)
2. Calls cmd.Help() to display the help
3. Returns fmt.Errorf("subcommand required") → exit code 1

SilenceUsage: true is set on both commands to prevent Cobra from double-printing the usage block after the returned error.

Before:

$ withings-export auth; echo "EXIT=$?"
Authentication commands
Usage:
  withings-export auth [command]
...
EXIT=0   ← misleading: scripts think auth succeeded

After:

$ withings-export auth; echo "EXIT=$?"
[help block → stderr, stdout is clean]
EXIT=1   ← correctly non-zero

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