Fix external file watching and add reload command (fixes #8)

[maxeonyx]

Problem

Out-of-workspace replacement files (configured via replacementsFiles) are loaded once at activation but never refreshed. vscode.workspace.createFileSystemWatcher only fires events for files inside a workspace folder, so changes to external config files (e.g. in dotfiles or home directories) are silently ignored until the user reloads the entire window.

Solution

• Add Node.js fs.watch() fallback for replacement files that resolve outside any workspace folder
• Add a Reload Replacement Files command for manual refresh
• Keep existing createFileSystemWatcher for in-workspace files (it works correctly there)

Fixes #8