Add place buttons to the agenda page

[JohanO]

Summary

• Adds a row of place buttons under each day's event list on the Agenda page
• Clicking a place creates a full-day, no-reminder, showAs: free event titled with the place name on the personal Microsoft (Graph) calendar
• Selecting a different place for the same day replaces the previous place event (radio-button semantics); clicking the already-active place is a no-op
• The place event itself is hidden from that day's event list (matched by title + calendar) since the button row already shows the selection

Implementation

• PlaceDayEvent entity + migration tracks which place is assigned to each day and its linked Graph event id
• GraphCalendarEventsClient gains CreateAllDayEventAsync/DeleteEventAsync (Graph integration was read-only before)
• PlaceEventsService resolves the personal Microsoft account (the one with Calendars.ReadWrite) and handles create/replace/no-op logic
• Home.razor renders the button row and wires it up

Test plan

• dotnet build — green
• Verified live: clicking a place creates the event immediately, switching places replaces the old event, re-clicking the active place is a no-op, selection survives a page reload
• Confirmed created/existing place events show as free in Outlook, not busy

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