feat: adaptive WebSocket reconnection with full-jitter backoff.

[real-venus]

Adaptive WebSocket Reconnection Stratum (#57)

Closes #57

File	Responsibility
src/types/connection.ts	Invariants (500 ms→30 s backoff ×2, 12-attempt cap, 15 s/5 s heartbeat, 500-frame buffer, sticky-node storage key) and the state/event/recovery-frame types.
src/utils/backoff.ts	backoffCeiling + fullJitterBackoff — AWS-style full jitter (random(0, min(cap, base·2^n))), overflow-safe, injectable RNG.
src/utils/frameBuffer.ts	500-slot circular buffer of telemetry frames; push/toArray/drain, evicts oldest, preserves the high-water sequence id across drains.
src/services/reconnectMachine.ts	Custom FSM: idle → connecting → connected with reconnecting / recovering / failed branches; computes the next jittered delay and declares terminal failure after 12 attempts. Pure transitions (the hook owns the timers) → fully unit-testable.
src/store/slices/connectionSlice.ts	Connection store (codebase's singleton pattern) + useConnectionState hook, with green/yellow/red quality derivation.
src/hooks/useWebSocket.ts	Delegates the lifecycle to the machine: full-jitter reconnect scheduling, heartbeat ping/pong watchdog, sticky nodeId in sessionStorage, recovery handshake (recovery → recovery_ack) replaying the buffer, and REST backfill (GET /ws/replay?from=&to=) when frames were missed. Injectable transport/clock/RNG/storage.
src/components/panels/ConnectionStatusBar.tsx	Fixed top bar (green/yellow/red) with attempt counter and a persistent terminal-failure banner + retry.
tests/unit/* + tests/hooks/useWebSocket.test.ts	Backoff bounds/cap, ring-buffer eviction/drain, FSM transitions + max-attempts→failed, slice/quality, and a fake-socket/fake-timer hook test covering connect, ping/pong, reconnect→recovery→backfill, heartbeat timeout, and terminal failure.