fix(ProcessManager): Linux home UI loading issue

[magicJie]

Summary

Fixes the issue where the OpenCode home UI cannot be loaded on Linux due to missing environment variables (especially PATH).

Problem

On Linux, spawning the OpenCode process directly doesn't inherit the user's shell environment, causing the server to fail to start properly.

Solution

Use an interactive login shell (/bin/bash -i -l) to spawn the process on non-Windows platforms:

• Linux/macOS: Use /bin/bash -i -l -c command to load the user's full environment (including PATH from .bashrc/.zshrc)
• Windows: Keep the original shell: true approach for .cmd file compatibility

Changes

• Platform-specific spawn logic in ProcessManager.start()
• Added environment variables (HOME, SHELL, TERM, XDG_CONFIG_HOME) for Linux/macOS
• Proper detached flag handling (false on Windows, true on Unix)

Testing

• Tested on Linux - server starts correctly, UI loads
• Windows compatibility preserved