Electron derives the userData path from productName in package.json,
which produces directories with spaces and parentheses on all platforms
(e.g. ~/.config/T3 Code (Alpha) on Linux). This is hostile to shell
usage and violates Linux XDG naming conventions.

Override the userData path via app.setPath() before the ready event to
use a clean lowercase name (t3code). If the legacy directory already
exists it is used as-is so existing users keep their Chromium profile
data (localStorage, cookies, sessions, cache).

This follows the same pattern VS Code uses — keeping productName for
display purposes while explicitly setting the data directory path.

Closes #578