fix(schedule): stop stray 'days' data from overriding Global schedule

save_schedule_config never persisted the schedule's 'mode' field, and
_check_schedule inferred per-day vs global purely from whether a 'days'
dict was present for the current day. Config migration
(_merge_template_defaults) re-adds the template's 'schedule.days' (all
days disabled by default) whenever it's missing from the user's saved
config - which is exactly the case after saving Global mode, since that
save path intentionally pops 'days'. The result: a user on Global mode
would get their schedule silently reinterpreted as per-day, with today's
day disabled, blanking the display.

Persist 'mode' on save and have _check_schedule honor it explicitly
(mirroring how _check_dim_schedule already does), so a resurrected
'days' dict can't override an explicit Global selection. Falls back to
the old inference behavior only when no 'mode' is recorded.

src/display_controller.py

@@ -621,18 +621,28 @@ class DisplayController:
 
         current_day = current_time.strftime('%A').lower()  # e.g. 'monday'
         current_time_only = current_time.time()
-        
+
         # Check if per-day schedule is configured
         days_config = schedule_config.get('days')
-        
-        # Determine which schedule to use
+
+        # Determine which schedule to use. Respect an explicit 'mode' field
+        # (like the dim schedule does) so a stray/legacy 'days' dict left over
+        # from config migration or a prior per-day setup can't silently
+        # override a user's Global schedule selection.
+        mode = schedule_config.get('mode')
+        mode_normalized = mode.replace('_', '-') if mode else None
+
         use_per_day = False
-        if days_config:
-            # Check if days dict is not empty and contains current day
-            if days_config and current_day in days_config:
+        if mode_normalized == 'global':
+            use_per_day = False
+        elif mode_normalized == 'per-day':
+            use_per_day = bool(days_config and current_day in days_config)
+        elif days_config:
+            # No explicit mode recorded (legacy config) - fall back to
+            # inferring from presence of a 'days' dict for the current day.
+            if current_day in days_config:
                 use_per_day = True
-            elif days_config:
-                # Days dict exists but doesn't have current day - fall back to global
+            else:
                 logger.debug("Per-day schedule exists but %s not configured, using global schedule", current_day)
         
         if use_per_day:

web_interface/blueprints/api_v3.py

@@ -329,6 +329,7 @@ def save_schedule_config():
         }
 
         mode = data.get('mode', 'global')
+        schedule_config['mode'] = mode
 
         if mode == 'global':
             # Simple global schedule