[Windows] Bring back persistent terminal sessions to eliminate flashing console windows

On Windows, each Bash/PowerShell tool call spawns a new console process, which causes a brief visible window flash. In a previous version, Claude Code kept two persistent terminal sessions (Bash + PowerShell) that could be minimized — all commands ran inside them without any flashing.

The current behavior is a cosmetic regression: the flashing windows are distracting, especially during intensive sessions with many tool calls.

Request: Add an option (or restore the previous default) to reuse persistent shell sessions instead of spawning a new process per command.

Environment:

• Platform: Windows 11 Pro
• Claude Code: Desktop app (latest)