This PR adds the TZ environment variable to ensure timezone-aware applications display the correct local time instead of UTC.

Problem

• Waybar clock format {:L%A %H:%M} displays UTC time instead of local time in some systems where TZ env variable is not defined
• Applications launched from shell don't inherit system timezone without TZ variable
• Users have to hardcode timezone in application configs as workaround

More details about the problem here #2170

Solution

• Dynamically set TZ environment variable based on system timezone via timedatectl
• Added to default/bash/envs so it's available in all bash sessions
• Works globally for all users without hardcoding timezone values

Testing

• Verified TZ variable is set correctly: echo $TZ shows system timezone
• Waybar clock now displays local time with :L locale operator
• Applications launched from shell inherit correct timezone

Fixes #2170