fix: prevent terminal output overflow when opening sftp

[qfxiongbinbin]

Problem

When a local terminal is printing a lot of output, such as while compressing a folder, opening the SFTP tab can lead to a white screen.

Root cause

Terminal output was being appended into React state on every chunk and kept growing without a strict cap. During heavy output, switching views could make the app render too much terminal history at once and destabilize the UI.

What changed

• Moved cached terminal output out of the React tab state into a dedicated ref map
• Added buffer caps to keep only a bounded amount of terminal history in memory
• Kept tab state updates focused on connection status instead of re-rendering on every output chunk
• Cleared the cached buffer when a terminal tab closes

Expected result

• Heavy terminal output no longer overwhelms the UI when switching to SFTP
• Terminal tabs still restore recent output, but with bounded memory usage