replace backend with stitch-wasm

[fabracht]

Replaces the TypeScript store backend with the Rust-backed @laboverwire/stitch-wasm. The TS package becomes a thin, framework-agnostic binding layer; all store/sync/persistence/queue logic now lives in stitch-rs (wasm).

Backend swap

• src/store.ts is now a thin adapter (StitchStore + MemoryView) over @laboverwire/stitch-wasm@0.2.1 — presents the exact Store interface the React/Vue bindings expect (property getters, config, version-cached memory shim, connection-status normalization, setReconnectValidator + getTicket-aware reconnect).
• Deleted relocated backend modules: memory-store, persistence-layer, remote-sync-layer, sync-engine, offline-queue, internal-utils, internal-wasm-error.
• types.ts/index.ts trimmed to the public surface; dropped create* internal factories, OwnershipError, MqdbError.
• Removed direct deps mqdb-wasm and mqtt5-wasm (now bundled inside the wasm).
• React/Vue bindings unchanged.

Pre-init tolerance

The wasm store throws not initialized before initialize() completes. React fires child effects before parent effects, and Vue's async init races the same way, so hooks/composables that subscribe or read on mount crashed. Fixed in the shared TS wrapper (not the Rust core — native async consumers can't hit this):

• sync reads gate on ready() and return empties ([]/{}/null/0/offline) instead of throwing;
• subscribe* defer wiring until a #readyPromise resolves, then poke the callback so useSyncExternalStore re-reads; deferred subs return a working unsubscribe;
• async methods route through #afterReady (run now if ready, else await init).

Tests

• Deleted obsolete backend tests (offline-queue-flush, response-topic-parse, wasm-error).
• Adapted integration tests to the wasm's async event delivery (vi.waitFor) and its subscribe-after-init contract.
• Added React (react-hook-init.test.tsx) and Vue (vue-composable-init.test.ts) coverage proving pre-init mounts don't throw and that a subscription established before init reactively receives data after init + scope load.
• vitest.config.ts gains vite-plugin-wasm + vite-plugin-top-level-await to load the wasm ESM.

Full suite: 30 passed. tsc, eslint, prettier clean.

Consumer note

Apps consuming this package will need vite-plugin-wasm (+ vite-plugin-top-level-await) in their Vite config to load the wasm ESM.