Cover ChatGPT auth failure and cancellation

[beiwei30]

Summary

• Add deterministic CLI E2E coverage for browser and device-login failure, timeout, and cancellation paths.
• Prove authentication state stays unchanged while callback listeners and helper processes are cleaned up.
• Harden OAuth response validation and keep provider-controlled errors bounded and redacted.

Verification

• cargo test -p orbcode --test chatgpt_auth_failure_e2e
• cargo test -p orbcode --test chatgpt_auth_browser_e2e --test chatgpt_auth_device_e2e
• cargo test -p orbcode-config openai_oauth
• cargo clippy -p orbcode-config -p orbcode --tests -- -D warnings
• scripts/check.sh
• git diff --check

Plan

Implements P1-03 from chatgpt-auth-p1-03-failure-cancellation-plan.md.

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