Fix VC Code and Zed install paths on Windows

[jimpark]

The existing Zed and VS Code detection/install/remove code used home_dir + "/.config/..." paths, which is Linux-specific.
On macOS it already had #ifdef APPLE with the Library/Application Support/ path, but there was no Windows case, and
the Linux fallback was hardcoded rather than respecting XDG_CONFIG_HOME.

What changed:

Two new platform helpers (cbm_app_config_dir(), cbm_app_local_dir()) return the OS-appropriate config directory:

• macOS: $HOME (callers append Library/Application Support/...)
• Linux: $XDG_CONFIG_HOME or ~/.config
• Windows: %APPDATA% / %LOCALAPPDATA%

Zed — 3 locations (detect, install, remove) now use:

• macOS: cbm_app_config_dir()/Library/Application Support/Zed/
• Windows: cbm_app_local_dir()/Zed/ (Zed stores config under %LOCALAPPDATA%)
• Linux: cbm_app_config_dir()/zed/

VS Code — 3 locations (detect, install, remove) now use:

• macOS: cbm_app_config_dir()/Library/Application Support/Code/User/
• Windows/Linux: cbm_app_config_dir()/Code/User/ (%APPDATA%/Code/User on Windows, ~/.config/Code/User on Linux)

Net effect: No behavior change on macOS or Linux (paths resolve identically). On Windows, Zed and VS Code config
directories are now found correctly instead of looking under the nonexistent ~/.config/ path.