Bug: split-pane launch fails with file not found due to invalid --direction flag for wt.exe

[wbreza]

Description

When dispatch is configured to open sessions in a terminal pane (launch_mode: pane), the launch fails with:

[error 2147942402 (0x80070002) when launching `down --startingDirectory ...`]
The system cannot find the file specified.

Root Cause

The code passes --direction <value> to wt.exe split-pane, but Windows Terminal's split-pane subcommand does not support a --direction flag. It uses -H (horizontal) and -V (vertical) instead.

Because --direction is unrecognized, Windows Terminal treats the direction value (e.g. down) as the command to execute in the new pane, resulting in a 'file not found' error.

Affected Code

• launchWindowsSession() in internal/platform/shell.go
• buildWSLWTArgs() in internal/platform/shell.go

Expected Behavior

Pane direction config values should be translated to the correct wt.exe flags:

• down / up -> -H (horizontal split)
• right / left -> -V (vertical split)
• auto -> no flag (let WT choose)