Improve frailbox logger error handling

[qingfeng312]

Summary

/claim #20

Improves frailbox legacy logger error handling so file-open, write, flush, and shutdown failures are reported clearly and degrade to stderr instead of silently dropping logs.

Payment address (USDC on Base): 0xe87b4889baeee4ed60a1b2bfc7b3a6a17bce4ad6

Changes

• Track the configured log file path for clearer diagnostics.
• Report log file open/write/flush/close failures with the failed operation and path.
• Fall back to stderr when a configured log file cannot be opened or later becomes unwritable.
• Add a focused C harness for logger open-failure, normal file logging, and write-failure fallback behavior.
• Document the logger fallback behavior in the operations guide.
• Commit the required diagnostic build artifacts.

Testing

• make -C frailbox logger-error-test passed.
• python3 build.py ran and produced the committed diagnostic artifacts.
• Build summary: frontend and v2-market-stream passed; the remaining modules failed because local prerequisites are unavailable (cargo, go, cmake, luac, ghc, Java runtime) or because of the existing frailbox MAP_HUGETLB portability issue.

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR
• Documentation has been updated, if applicable
• Configuration or schema changes are documented, if applicable
• No generated build artifacts are committed, except the required diagnostic build log
• Changes are scoped to the PR purpose and avoid unrelated cleanup
• Security, privacy, and error-handling implications have been considered

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• I would like to request that my diagnostic build log is removed before merging