Add unified useSyncStatus hook

[KidkArolis]

What changed

• add a canonical figbird.sync tracker and React useSyncStatus() hook
• expose phase, pending/failed write counts, fetching query count, pending reconciliation count, and lastSyncedAt
• track Socket.IO connection changes, reconnect jitter, hidden-tab reconciliation, query retries, ordinary mutations, and paused mutation queues
• export the hook standalone and from createHooks(schema)
• showcase the state in the demo navigation with offline, restoring, saving, error, and saved labels
• document the API and adapter connection-state extension points

Why

Applications currently have to combine query state, useMutating(), mutation queue state, reconnect behavior, and observability events to answer a basic UI question: “is my data synchronized?” Events are intentionally non-replaying, so they cannot provide canonical state to components that mount mid-operation.

The new tracker is maintained synchronously alongside Figbird’s query and mutation state. Subscribers therefore receive the correct snapshot even when they mount during a fetch, queued write, disconnect, retry, or deferred reconciliation.

Validation

• npm run test — 350 tests passing (typecheck, lint, Prettier, AVA)
• npm --prefix demo exec tsc -- --noEmit
• demo production build with Vite