fix(selfhost): surface codex auth expiry errors faster

[sentry]

Summary

This PR addresses the selfhost_ai_providers_exhausted: codex_timeout error, which was found to be a symptom of expired Codex authentication. Previously, an expired Codex token would cause the codex CLI to hang indefinitely, leading to a 10-minute timeout before the error was reported. This fix implements a two-pronged approach:

1. Preflight token expiry check: The assertCodexAuthConfigured function now parses auth.json to check the token's expires_at field. If expired, it immediately throws a codex_no_auth error before the codex subprocess is spawned.
2. Improved timeout error handling: In the timedOut error path within createCodexAi, if the codex CLI times out and its stderr contains "Reading prompt from stdin...", it is now re-thrown as a codex_no_auth error.

These changes ensure that expired Codex authentication is detected and reported quickly and clearly, preventing long timeouts and providing immediate guidance to re-run codex auth.

Scope

• The PR title follows type(scope): short summary Conventional Commit format, for example fix(api): restore profile access checks.
• This PR is focused and does not mix unrelated backend, UI, MCP, docs, dependency, and deploy changes.
• This follows CONTRIBUTING.md and does not reintroduce GitHub Pages, VitePress, site/, or CNAME.
• I linked an issue, or this is small enough that the summary explains why an issue is not needed.

Validation

• git diff --check
• npm run actionlint
• npm run typecheck
• npm run test:coverage locally; codecov/patch requires ≥99% coverage of the lines AND branches you changed (aim for 100% on your diff so CI variance does not fail near the threshold). Global coverage is a non-blocking trend with a loose 90% backstop, not the gate.
• npm run test:workers
• npm run build:mcp
• npm run test:mcp-pack
• npm run ui:openapi:check
• npm run ui:lint
• npm run ui:typecheck
• npm run ui:build
• npm audit --audit-level=moderate
• New or changed behavior has unit/integration tests for new branches, fallback paths, and sanitizer boundaries

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• API/OpenAPI/MCP behavior is updated and tested where needed.
• UI changes use live API data or real empty/error/loading states, not production mock/demo fallbacks.
• Visible UI changes include a UI Evidence section below with JPG/JPEG or PNG screenshots arranged as organized, captioned, clickable thumbnails. SVG screenshots are not used as review evidence. Review-only screenshots or recordings are not committed to the repository.
• Public docs/changelogs are updated where needed; changelogs are only edited for release-prep PRs.

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State / title	JPG/PNG evidence
Loaded state	<a href="FULL_URL.png"><img src="FULL_URL.png" alt="Loaded state" width="240"></a>
Empty/error/mobile state, if relevant

Notes

Fixes GITTENSORY-M

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

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[loopover-orb]

Gittensory is closing this pull request on the maintainer's behalf (CI is failing (validate, validate-code)). This is an automated maintenance action — to pursue this change, please open a new pull request with the issues resolved. Closed PRs may be analyzed later to improve review accuracy, but they are not automatically reopened or re-reviewed.