feat: high-resolution timer wheel for scheduled Soroban executions (#56)

[real-venus]

High-Resolution Timer Wheel for Scheduled Soroban Executions (#56)

Closes #56

What's included

File	Responsibility
src/types/scheduler.ts	Invariants (1024 slots × 100 ms ≈ 102.4 s span, 1,000-job cap, ±50 ms tolerance, 200 ms fallback), job/meta/status types, the SAB Int32 layout, and the worker protocol.
src/utils/sharedBuffer.ts	SharedArrayBuffer creation + atomic drift/heartbeat/command accessors, COOP/COEP availability check, and futexWait/futexNotify that degrade safely on a non-shared buffer.
src/utils/timerWheelCore.ts	The pure hashed wheel: jobs hashed into slots with a rounds counter for >1-rotation targets, and a pending set so sub-slot jobs are never skipped. schedule/cancel/advance with recurrence, drift correction, missed-fire detection, and the 1,000-job cap.
src/workers/timerWheel.worker.ts	Holds the wheel and sleeps each tick on Atomics.wait(HEARTBEAT, …, 100ms) (woken early by command notifies; timed-loop fallback without SAB), advances using Date.now(), and posts fired jobs.
src/services/timerWheel.ts	Main-thread facade: worker path or a 200 ms polling fallback, plus a requestAnimationFrame loop that writes a drift correction into the buffer while the tab is hidden.
src/hooks/useScheduledExecution.ts	Wraps the service, mirrors metadata into the store, and auto-cancels on unmount.
src/store/slices/scheduleSlice.ts	Job metadata (next fire, status, missed count) with selectors.
src/components/dashboard/SchedulerDashboard.tsx	Jobs table (name / next fire / interval / status / missed / cancel).
tests/unit/*	Wheel ordering, rounds, recurrence (no catch-up storm), cancel, capacity, precision/missed, drift; atomic buffer round-trips; and the schedule store.