Add runnable WebSocket sync example

[pttydou]

What & why

Fixes #4.

Adds a runnable sync workspace with two boards connected through a byte-only WebSocket relay. Local user diffs are broadcast with the store's source filter, and received diffs are applied as remote so each client's undo history stays local. This v1 example uses record-level last-writer-wins and intentionally has no persistence or CRDT.

Verified with npm test, npm run typecheck, npm run build, and a two-client Edge browser smoke test.

Checklist

• Tests added or updated (npm test passes)
• Type declarations updated if the public API changed (npm run typecheck)
• RN WebView bundle regenerated if core changed (npm run build)
• No new runtime dependencies in @quickdrawjs/core

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[nmndwivedi]

Clean, self-contained example: relay is byte-only, path traversal is guarded, and the undo-isolation test covers the important bit. Lockfile change is just the workspace link (ws was already in the tree). Tests + typecheck pass on top of current main. Thanks!