feat: Refactor template handling, improve scheduler functions, and add timezone utilities

- Moved Jinja2 template setup to a shared configuration file (templates_config.py) for consistent usage across routers.
- Introduced timezone utilities in a new module (timezone.py) to handle UTC to local time conversions and formatting.
- Updated all relevant routers to use the new shared template configuration and timezone filters.
- Enhanced templates to utilize local time formatting for various datetime fields, improving user experience with timezone awareness.

templates/partials/slm_device_list.html

@@ -51,7 +51,7 @@
 
             <div class="mt-2 text-xs text-gray-500 dark:text-gray-400">
                 {% if unit.slm_last_check %}
-                    Last check: {{ unit.slm_last_check.strftime('%Y-%m-%d %H:%M') }}
+                    Last check: {{ unit.slm_last_check|local_datetime }}
                 {% else %}
                     No recent check-in
                 {% endif %}