feat: add timezone support for schedules and dim schedule feature (#218)

* feat: add timezone support for schedules and dim schedule feature

- Fix timezone handling in _check_schedule() to use configured timezone
  instead of system time (addresses schedule offset issues)
- Add dim schedule feature for automatic brightness dimming:
  - New dim_schedule config section with brightness level and time windows
  - Smart interaction: dim schedule won't turn display on if it's off
  - Supports both global and per-day modes like on/off schedule
- Add set_brightness() and get_brightness() methods to DisplayManager
  for runtime brightness control
- Add REST API endpoints: GET/POST /api/v3/config/dim-schedule
- Add web UI for dim schedule configuration in schedule settings page

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix: normalize per-day mode and validate dim_brightness input

- Normalize mode string in _check_dim_schedule to handle both "per-day"
  and "per_day" variants
- Add try/except around dim_brightness int conversion to handle invalid
  input gracefully

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* refactor: improve error handling in brightness and dim schedule endpoints

- display_manager.py: Add fail-fast input validation, catch specific
  exceptions (AttributeError, TypeError, ValueError), add [BRIGHTNESS]
  context tags, include stack traces in error logs
- api_v3.py: Catch specific config exceptions (FileNotFoundError,
  JSONDecodeError, IOError), add [DIM SCHEDULE] context tags for
  Pi debugging, include stack traces

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Chuck <chuck@example.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

web_interface/blueprints/pages_v3.py

@@ -140,8 +140,13 @@ def _load_schedule_partial():
         if pages_v3.config_manager:
             main_config = pages_v3.config_manager.load_config()
             schedule_config = main_config.get('schedule', {})
+            dim_schedule_config = main_config.get('dim_schedule', {})
+            # Get normal brightness for display in dim schedule UI
+            normal_brightness = main_config.get('display', {}).get('hardware', {}).get('brightness', 90)
             return render_template('v3/partials/schedule.html',
-                                 schedule_config=schedule_config)
+                                 schedule_config=schedule_config,
+                                 dim_schedule_config=dim_schedule_config,
+                                 normal_brightness=normal_brightness)
     except Exception as e:
         return f"Error: {str(e)}", 500