fix: preserve Codex rows on refresh errors

[ericweichun]

Summary

• keep the early Codex quota rows when the later full refresh path fails
• preserve Codex session / weekly rows and stale metadata in the error state instead of clearing the Codex section to missing
• add a regression test for a failed full refresh after the early Codex quota update

Context

#24 preserved the menu-bar Codex percentage during refresh failures, but the popover state still came from _error_state(), which reset the Codex rows to missing. This follow-up keeps the Codex rows that were already loaded at the start of the refresh.

Tests

• .venv/bin/ruff check .
• .venv/bin/mypy .
• .venv/bin/python -m pytest tests/ -q