Use server-side date filtering for device event history chart

The device event history chart previously fetched all events and filtered
client-side. This wires the existing created_from API parameter to the
frontend so filtering happens in the backend.

Also fixes a bug where the Today filter returned no results: rusqlite was
storing datetimes with a space separator ("YYYY-MM-DD HH:MM:SS+00:00")
while SQL filters used RFC 3339 with a T separator, causing string
comparisons to fail for same-day events. All datetime storage across
device_events, devices, and notifications is now consistently RFC 3339.
A migration converts existing records.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/lib/devices/device_event_history.dart

@@ -70,7 +70,7 @@ class DeviceEventHistory extends StatefulWidget {
 }
 
 class _DeviceEventHistoryState extends State<DeviceEventHistory> {
-  List<DeviceEvent>? _allEvents;
+  List<DeviceEvent>? _events;
   bool _isLoading = true;
   String? _error;
   _TimeRange _selectedRange = _TimeRange.lastWeek;
@@ -89,10 +89,11 @@ class _DeviceEventHistoryState extends State<DeviceEventHistory> {
     try {
       final events = await BackendAPI.instance.getDeviceEvents(
         widget.device.macAddress,
+        createdFrom: _selectedRange.cutoff,
       );
       if (!mounted) return;
       setState(() {
-        _allEvents = events;
+        _events = events;
         _isLoading = false;
       });
     } catch (e) {
@@ -104,12 +105,6 @@ class _DeviceEventHistoryState extends State<DeviceEventHistory> {
     }
   }
 
-  List<DeviceEvent> get _filteredEvents {
-    if (_allEvents == null) return [];
-    final cutoff = _selectedRange.cutoff;
-    return _allEvents!.where((e) => e.createdOn.isAfter(cutoff)).toList();
-  }
-
   @override
   Widget build(BuildContext context) {
     if (_isLoading) {
@@ -126,7 +121,7 @@ class _DeviceEventHistoryState extends State<DeviceEventHistory> {
       );
     }
 
-    final events = _filteredEvents;
+    final events = _events ?? [];
 
     return Column(
       crossAxisAlignment: CrossAxisAlignment.start,
@@ -143,6 +138,7 @@ class _DeviceEventHistoryState extends State<DeviceEventHistory> {
             selected: {_selectedRange},
             onSelectionChanged: (selection) {
               setState(() => _selectedRange = selection.first);
+              _loadEvents();
             },
           ),
         ),

frontend/lib/utils/oott_api.dart

@@ -137,9 +137,19 @@ class BackendAPI {
     await _dio.delete('/devices/$macAddress');
   }
 
-  Future<List<DeviceEvent>> getDeviceEvents(String macAddress) async {
+  Future<List<DeviceEvent>> getDeviceEvents(
+    String macAddress, {
+    DateTime? createdFrom,
+  }) async {
     debugPrint('About to call GET /devices/$macAddress/events');
-    final response = await _dio.get('/devices/$macAddress/events');
+    final queryParams = <String, dynamic>{};
+    if (createdFrom != null) {
+      queryParams['created_from'] = createdFrom.toUtc().toIso8601String();
+    }
+    final response = await _dio.get(
+      '/devices/$macAddress/events',
+      queryParameters: queryParams.isEmpty ? null : queryParams,
+    );
     debugPrint('Received: ${response.data}');
     return (response.data as List)
         .map((item) => DeviceEvent.fromJson(item as Map<String, dynamic>))