fix(snapshot): clarify remote rollback limitations

[bobleer]

Summary

• disable rollback and edit-and-rerun for remote workspace sessions because remote file snapshots are not recorded
• reject remote rollback atomically in Desktop and CLI before task cancellation, file changes, or history deletion
• show explicit localized guidance and classify rollback commands as RemoteUnsupported

Verification

• pnpm run type-check:web
• pnpm --dir src/web-ui run test:run src/flow_chat/components/modern/UserMessageItem.test.tsx
• pnpm run i18n:audit
• cargo test -p bitfun-desktop snapshot_service::tests
• cargo test -p bitfun-desktop complete_rollback_commands_explicitly_reject_remote_workspaces
• cargo test -p bitfun-desktop desktop_runtime_wiring_reuses_existing_core_owners
• cargo test -p bitfun-cli peer_host::commands::snapshot::tests
• cargo check -p bitfun-desktop -p bitfun-cli