Fix Ozwell timer clock guard for teamless events and clean clock test teardown

[Copilot]

This addresses two review-thread regressions from PR #231: Ozwell incorrectly rejected ticket timer starts after user-scoped clock_in, and backend/tests/clock.test.ts teardown could leave fixture clock events behind.

• Ozwell ticket timer: accept user-scoped active clock events

  • Updated start_ticket_timer validation to allow an active clock event with no teamId (new contract) while still rejecting mismatched explicit team-scoped events.
  • Kept existing ticket/team ownership checks intact.

• Backend clock test teardown: clean all fixture users

  • Added otherId fixture capture.
  • Changed teardown clockevents cleanup from team-based delete to fixture-user-based delete so teamless events are also removed.

// before
if (ctx.activeClockEvent.teamId !== teamId) { ... }

// after
if (ctx.activeClockEvent.teamId && ctx.activeClockEvent.teamId !== teamId) { ... }

[mfisher31]

cherry picked in to #231 , closing.