credits user: UnexpectedError when the profile is open in the user's own Chrome #984

Observed (2026-10-15, develop code path)

gflow credits user --profile <p> --json, run while a plain Chrome window (not gflow) has that profile's directory open, exits 1 with:

{"status": "fail", "error": {"class": "UnexpectedError", "title": "Unexpected error", "exit_code": 1}}

Log trail: cookie_decryption_failed_falling_back_to_playwright → credits.http_fallback_to_browser error_type=TargetClosedError → client.preread_flow_cookies_failed → error_unhandled.

The crash is in the browser fallback at src/gflow_cli/services/credits.py:51 on develop. The Playwright launch exits because Chrome's own SingletonLock is held; ProfileLease cannot see a non-gflow Chrome.

Expected

A typed, actionable error, e.g. "profile is open in another Chrome window — close it and retry", not an UnexpectedError. Ideally exit 11 like ProfileLockedError.

Repro

1. Pick a profile whose cookie decrypt falls back to Playwright.
2. Start chrome.exe --user-data-dir=<profile_dir> about:blank.
3. Run gflow credits user --profile <name> --json.

Found while spiking PR #982, which has the same class of defect in auth/renew.py:107 (reported there). A shared fix for "Chrome launch refused because the profile is held outside gflow" probably belongs in one launch helper.