Fix flaky threshold test in extraction-manager

[rjroy]

Problem

The test needsCatchUp edge cases > handles exactly at threshold is flaky and failed in CI.

Root Cause

The test calculates exactlyAtThreshold using Date.now(), then needsCatchUp() internally calls Date.now() again. If even 1ms passes between those calls, the elapsed time exceeds the threshold and the test fails.

const exactlyAtThreshold = new Date(Date.now() - DEFAULT_CATCHUP_THRESHOLD_MS).toISOString();
// ... time passes ...
expect(needsCatchUp(state)).toBe(false);  // needsCatchUp calls Date.now() again

Fix

Inject a clock/time provider into needsCatchUp() so tests can control time deterministically.

Acceptance Criteria

• Test passes reliably (no timing dependency)
• needsCatchUp() accepts optional now parameter or clock injection
• Existing behavior unchanged when no clock provided

References

• CI failure in PR fix: Send select_vault on each WebSocket connection #383

[rjroy]

Fake timers migration completed in commit a34236c (2026-01-23). Systematic fix for Date.now() timing issues applied.