fix: add Windows compatibility for terminal width detection

[ItsDaRa]

Summary

• Adds Windows platform check to getTerminalWidth() and canDetectTerminalWidth() in src/utils/terminal.ts
• Uses process.stdout.columns on Windows instead of Unix-only shell commands

Problem

On Windows, the current terminal width detection causes issues:

• tput command doesn't exist
• ps, stty, awk are Unix-only utilities
• Shell redirect 2>/dev/null creates a literal file named "null" in the working directory instead of suppressing stderr

This results in spurious "null" files being created wherever Claude Code is run.

Solution

Added a platform check at the start of both functions:

if (process.platform === 'win32') {
    const cols = process.stdout.columns;
    // return width or null/boolean as appropriate
}

process.stdout.columns is the Node.js cross-platform API for terminal width and works reliably on Windows.

Test plan

• Tested on Windows 11 - no more "null" files created
• Terminal width detection works correctly
• Unix behavior unchanged (early return on Windows means Unix code path untouched)

Fixes #117

🤖 Generated with Claude Code

[sirmalloc]

@ItsDaRa Have you tested this and seen the terminal width return appropriately on Windows? The main issue has always been that Claude Code calls the statusline as a subprocess without an actual connection to the terminal Claude Code is running in, so typical width detection always returns 80. If you can verify this by adding the "terminal width" widget to your statusline and resizing the terminal and verify it updates properly, then I'll merge this and push a new build out. I don't currently have a Windows machine easily accessible.