fix(dashboard): sidebar theming, calendar reactivity, and booking filters

Fix multiple dashboard and UI issues:

Frontend fixes:
- Fix sidebar remaining dark on light theme (add proper light/dark CSS variables)
- Fix DashboardCalendar blank/not showing events (use watch + calendar API instead of computed options)
- Fix upcoming bookings to include active and recent past (last 7 days) bookings
- Improve sidebar collapsed state UX (stack footer buttons vertically, full width)

Details:
- theme.css: Add light sidebar colors (white bg) for :root, keep dark colors for [data-theme="dark"]
- DashboardCalendar: Add watch on events, use calendarRef to update events via removeAllEvents/addEventSource
- Dashboard: Change upcoming filter from "startDate >= now" to "endDate >= 7 days ago"
- AppSidebar: Stack footer-actions vertically when collapsed for better visibility

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

frontend/src/views/Dashboard.vue

@@ -181,13 +181,18 @@ const adminStats = computed(() => {
   }
 })
 
-// Get upcoming bookings (approved or pending, sorted by start time)
+// Get upcoming bookings (active, future, and recent past - last 7 days)
 const upcomingBookings = computed(() => {
   const now = new Date()
+  const sevenDaysAgo = new Date(now.getTime() - 7 * 24 * 60 * 60 * 1000)
+
   return myBookings.value
     .filter((b) => {
-      const startDate = new Date(ensureUTC(b.start_datetime))
-      return startDate >= now && (b.status === 'approved' || b.status === 'pending')
+      if (b.status !== 'approved' && b.status !== 'pending') return false
+
+      const endDate = new Date(ensureUTC(b.end_datetime))
+      // Include if not ended yet OR ended within last 7 days
+      return endDate >= sevenDaysAgo
     })
     .sort((a, b) => {
       return new Date(ensureUTC(a.start_datetime)).getTime() - new Date(ensureUTC(b.start_datetime)).getTime()