Add a lightweight discrete tick-based clock for synchronized multi-agent
simulation (issue #633). Agents all act on the same tick, world updates,
then the clock advances to the next tick.
- SimulationClock: advance(), elapsed(), reset(), wait_for_tick(),
record_snapshot(), get_snapshots(), get_snapshot_at()
- TickSnapshot: per-tick world state record for replay/analysis
- DependencyScheduler: optional tick-synchronized dispatch mode via
run_tick_synchronized() that dispatches all ready tasks per tick,
waits for completion, records snapshots, then advances the clock
- MCTaskExecutor: injects simulation_tick into task prompt when present
in task metadata
- Exported SimulationClock and TickSnapshot from deep_work package
- 17 new tests covering clock, snapshots, scheduler integration, and
prompt injection
