fix: Add lock file to omarchy-cmd-tzupdate

[guilhermetk]

This PR improves the timezone update script by adding:

• A lockfile mechanism to prevent concurrent runs
• Automatic cleanup with trap
• Handling of stale lockfiles (5 min expiry)

Without this, repeated right clicks on the clock may result in multiple Waybar instances:

[abenz1267]

Why is that script even a thing on right-click to begin with?

[guilhermetk]

It’s a chef’s addition: eace29a. Maybe because he travels frequently, but that’s just a guess.

Edit: here it is: #314 (comment)