fix(util): tighten const usage and pthread format (tracking issue)

[somethingwithproof]

Summary

Track and review the work in PR #454.

Follow-up PR for warning cleanup outside #452 scope.\n\nChanges:\n- make read_spine_config take a const file path in util.h and util.c\n- fix pthread_self log format specifier to match cast type (%lu)\n\nValidation:\n- change is minimal and isolated\n- local configure/build could not complete in this environment due missing MySQL headers

Scope

• Validate implementation and CI results
• Address review feedback
• Merge PR fix(util): tighten const usage and pthread format #454 and close this issue via linkage

Acceptance Criteria

• Scope checklist is complete.
• Linked pull request is merged.

Linked Pull Request

• fix(util): tighten const usage and pthread format #454