fix: replace Column+Expanded with CustomScrollView on calendar screen

The mobile calendar layout had a split-height bug where the event list
at the bottom was squeezed into whatever pixel crumbs remained after the
calendar card and summary bar consumed their fixed space. On small phones
or 6-row months (~390px calendar), the events area could shrink to under
100px — barely one card, with no way to scroll.

Fix: replace Column + Expanded(ListView) with a CustomScrollView using
slivers so the full page — calendar card, summary bar, and event cards —
scrolls as one unified surface. SliverFillRemaining handles loading and
empty states so they always fill the visible viewport naturally.

lib/screens/calendar_screen.dart

@@ -637,32 +637,54 @@ class _CalendarScreenState extends State<CalendarScreen> {
             ),
           ),
 
-          // CONTENT: calendar card overlapped on gradient, then summary and list
-          Column(
-            children: [
-              const SizedBox(height: 110), // leave space for appbar + some gradient top
-              _calendarCard(context), // calendar card sits visually on top of the gradient
-              _selectedDateSummary(context),
-              Expanded(
-                child: _loadingDay
-                    ? Center(child: CircularProgressIndicator(color: theme.colorScheme.primary))
-                    : _eventsOfDay.isEmpty
-                        ? Center(
-                            child: Column(
-                              mainAxisSize: MainAxisSize.min,
-                              children: [
-                                Icon(Icons.event_available, size: 48, color: theme.hintColor),
-                                const SizedBox(height: 10),
-                                Text('No events scheduled for this date', style: theme.textTheme.bodyMedium?.copyWith(color: theme.hintColor)),
-                              ],
-                            ),
-                          )
-                        : ListView.builder(
-                            padding: const EdgeInsets.only(top: 6, bottom: 32),
-                            itemCount: _eventsOfDay.length,
-                            itemBuilder: (context, idx) => _eventCardMobile(_eventsOfDay[idx]),
-                          ),
-              ),
+          // CONTENT: whole page scrolls as one — calendar + summary + events
+          CustomScrollView(
+            physics: const BouncingScrollPhysics(),
+            slivers: [
+              // Space for app bar + gradient top
+              const SliverToBoxAdapter(child: SizedBox(height: 110)),
+
+              // Calendar card
+              SliverToBoxAdapter(child: _calendarCard(context)),
+
+              // Selected date summary
+              SliverToBoxAdapter(child: _selectedDateSummary(context)),
+
+              // Events area — loading / empty / list
+              if (_loadingDay)
+                SliverFillRemaining(
+                  hasScrollBody: false,
+                  child: Center(
+                    child: CircularProgressIndicator(color: theme.colorScheme.primary),
+                  ),
+                )
+              else if (_eventsOfDay.isEmpty)
+                SliverFillRemaining(
+                  hasScrollBody: false,
+                  child: Center(
+                    child: Column(
+                      mainAxisSize: MainAxisSize.min,
+                      children: [
+                        Icon(Icons.event_available, size: 48, color: theme.hintColor),
+                        const SizedBox(height: 10),
+                        Text(
+                          'No events scheduled for this date',
+                          style: theme.textTheme.bodyMedium?.copyWith(color: theme.hintColor),
+                        ),
+                      ],
+                    ),
+                  ),
+                )
+              else
+                SliverList(
+                  delegate: SliverChildBuilderDelegate(
+                    (context, idx) => _eventCardMobile(_eventsOfDay[idx]),
+                    childCount: _eventsOfDay.length,
+                  ),
+                ),
+
+              // Bottom padding
+              const SliverToBoxAdapter(child: SizedBox(height: 32)),
             ],
           ),
         ],