fix: use interactive exec for custom command execution

[amitksingh1490]

Summary

Fix custom command execution to use interactive exec, ensuring proper terminal handling when running custom commands through the shell plugin.

Context

When executing custom commands via the shell plugin's dispatcher (:command syntax), the _forge_exec function was being used instead of _forge_exec_interactive. This meant custom commands were missing interactive terminal capabilities (like proper pty handling, signal forwarding, and real-time output streaming) that are already present for default agent execution at dispatcher.zsh:82.

Changes

• Replaced _forge_exec calls with _forge_exec_interactive in the custom command branch of _forge_action_default
• Applies to both the case with input text and without input text

Key Implementation Details

The _forge_exec_interactive function provides a proper interactive terminal session with pty support, while _forge_exec is a simpler non-interactive execution. Custom commands benefit from the same interactive capabilities as the default agent path, which already uses _forge_exec_interactive.

Testing

# Source the updated shell plugin
source shell-plugin/lib/dispatcher.zsh

# Run a custom command (requires a custom command to be defined)
# Verify output streams properly with real-time display
:my-custom-command some input text

# Verify without input text
:my-custom-command