fix(providers): preserve Codex SSE error details

[fancyboi999]

Summary

• Preserve bounded type, code, and message details from Codex error and response.failed SSE events.
• Map Codex capacity failures into the existing transient server classification so the normal retry and fallback ladder applies.
• Ignore nested payload fields, remove control characters, and bound logged values instead of serializing the full remote event.

Type

• Fix
• Feature
• Docs
• CI / tooling
• Refactor
• Other

Verification

• uv run pytest tests/test_openai_codex_provider.py tests/test_error_classification.py tests/test_provider_fallback_chain.py -q: 53 passed.

• uv run --all-extras pytest -q --deselect tests/test_cli_theme.py::test_bold_accent_renders_styled_not_bare: 5158 passed, 30 skipped, 14 deselected, 2 warnings.

• uv run --extra dev ruff check raven/providers/openai_codex_provider.py tests/test_openai_codex_provider.py: passed.

• uv run --extra dev ruff format --check raven/providers/openai_codex_provider.py tests/test_openai_codex_provider.py: passed.

• uv run pre-commit run --files raven/providers/openai_codex_provider.py tests/test_openai_codex_provider.py: passed.

• Live OAuth call through OpenAICodexProvider.chat_with_retry() using an account-advertised Codex model returned finish_reason=stop and the expected RAVEN_E2E_OK response.

• make ci reaches one pre-existing tests/test_cli_theme.py::test_bold_accent_renders_styled_not_bare failure reproduced unchanged on a clean origin/main worktree. The remaining TUI tests and builds passed when run separately.

• Relevant tests pass locally

• Relevant lint / type checks pass locally

• User-facing docs or screenshots are updated when needed

No user-facing documentation describes this internal error representation, so no documentation or screenshots were changed.

Risk

• Error output changes from a fixed generic string to bounded structured fields for Codex SSE failures.

• Unrelated and malformed failures retain non-retryable or generic behavior, and the change can be rolled back by reverting this PR.

• Security impact considered

• Backward compatibility considered

• Rollback path is clear for risky changes

Related Issues

Fixes #234