fix: keep structured logs when --quiet is set

[Firehed]

Fixes #2693.

With --structured-logs and --quiet both set, the structured logger was created and then replaced by the plain-text quiet logger, so errors were written as plain text instead of JSON. NewStructuredLogger already takes quiet and drops info-level output itself, so the plain-text quiet logger is now only used when structured logs are off.

This restores the behavior from #1750 (the fix for #1738), which was lost when the logger setup moved in #2106. The new test covers the combined flags so this doesn't regress again.

🤖 Generated with Claude Code

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[kgala2]

/gcbrun

[kgala2]

Thanks @Firehed for tracking this regression back to #2106 and adding a test to guard it, LGTM.

One blocker: the CLA check is failing on the Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com trailer (your own CLA is fine). Could you drop that trailer from both commits and force-push? The check should go green after that.

[Firehed]

@kgala2 force push is done and I now see the CLA check passing. Let me know if you need anything else!

[kgala2]

/gcbrun