feat(harmonyos): browse remote workspace folders

[wgqqqqq]

Summary

• replace the recent-workspace picker behind the sidebar workspace add action with a real remote directory browser
• add a capability-negotiated list_directories Remote Connect command with bounded, directory-only results
• start browsing from the target device home directory, support parent and child navigation, and switch workspace only after explicit confirmation
• show a clear upgrade-required state for older hosts instead of silently falling back to recent workspaces
• keep QR-paired and same-account device capability state isolated across target switches

Verification

• cargo test -p bitfun-services-integrations --features remote-connect remote_workspace_handler_lists_only_remote_directories
• cargo test -p bitfun-services-integrations --features remote-connect directory_browser_wire_shapes_are_backward_compatible
• cargo check -p bitfun-services-integrations --no-default-features
• HarmonyOS LocalTest
• HarmonyOS assembleHap
• pnpm run harmony:architecture
• pnpm run check:core-boundaries

Remote scenarios

• Remote control: verified the older-host downgrade UI on a real HarmonyOS device
• Cross-version compatibility: legacy responses deserialize without capabilities, and the phone gates the new command on workspace_directory_browser_v1
• Remote workspace, Peer Device Mode, and Detached Dispatch behavior are unchanged