Move RSpaceOfflineRuntime, CommunitySync, OfflineStore, and
RStackHistoryPanel into a new shell-offline.ts chunk loaded via
dynamic import(). This removes ~2.5MB of Automerge WASM from the
critical path, reducing blocking JS from ~960KB to ~150KB brotli.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
