fix(coding-agent): stabilize macOS process identity

[chai1any]

Summary

• run the portable ps -o lstart= process identity query with TZ=UTC and LC_ALL=C
• preserve the caller environment while making daemon start IDs stable across macOS timezone and locale changes
• add regression coverage for the fixed query environment

Verification

• npx tsx ../../node_modules/vitest/dist/cli.js --run test/daemon-ps.test.ts (24 tests passed)
• npm run check
• manually queried the current PID after switching process.env.TZ between America/Los_Angeles and Asia/Kolkata; both IDs were identical

Fixes #879

Note

Fix macOS process identity invalidation caused by timezone changes

• On macOS, getProcessStartId in session-lease.ts uses ps to derive a stable process start identifier, but the output varies with system timezone or locale, causing the running daemon's identity to change.
• Extracts the ps call into a new getPsProcessStartId helper that forces TZ=UTC and LC_ALL=C in the subprocess environment, ensuring a consistent output regardless of system settings.
• Extends runProcessQuery to accept an optional env override so callers can supply a custom environment without affecting the default behavior.

^{Macroscope summarized 7053d4f.}