Centralizes engine tuning values, poll intervals, logfmt column
regex fragments, and app/settings identity strings that were
previously defined ad hoc across engine.rs, ingest.rs, logfmt.rs,
profile.rs, settings.rs, and main.rs.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A1ZJ3SrayzLzVndhVq9BmS
