feat: SSH/SFTP usability and reliability improvements

[qfxiongbinbin]

Summary

• SFTP path bar: commits on Enter/blur instead of firing one remote directory listing per keystroke (both SFTP panes and the local file navigator)
• Delete confirmation: local/remote file deletion now shows a confirmation dialog with the full path before executing
• Disconnect awareness: the Rust backend emits a structured terminal-exit event; the UI flips the tab to a disconnected state and offers an in-place Reconnect that reuses the same tab (same host, or same cwd for local shells)
• SSH connection reuse: ssh/sftp/monitor commands share one authenticated connection per host via OpenSSH ControlMaster multiplexing (sockets in ~/.serverdeck/cm, ControlPersist 60s) — repeat SFTP navigation and monitor refreshes skip TCP+auth entirely
• Also carries the local terminal scroll stability fix this branch was created for, plus pending AI memory files work (scan/read agent memory files in settings)

Test plan

• cargo check and npm run tauri dev
• SFTP: typing in the path bar does not trigger listings; Enter/blur does; Esc restores
• Right-click delete (local and remote) shows the confirmation dialog; cancel does nothing
• Kill an SSH session server-side: tab dot turns grey, overlay offers Reconnect, reconnect restores the session in the same tab
• Open a terminal to a host, then browse SFTP on the same host: no second authentication, listings are fast

🤖 Generated with Claude Code

https://claude.ai/code/session_015R3DVRqVdvkiD6YVchgcBv