feat(sharedb): add bounded stale resync and websocket submit protocol

[edocevol]

Summary

• add bounded stale rebase/resync handling to sharedb submit flow
• add websocket submit/submit_ack/submit_error protocol with session-bound identity checks
• expand stale rebase, replay, rollback, page-block, and websocket protocol tests

Test Plan

• cd sharedb && go test ./...
• cd sharedb && go vet ./...
• cd sharedb && go test -race ./...
• go test ./...