feat: complete calendar integration with UI improvements and code cleanup

Calendar Integration Tasks:
- Update upcoming meetings window from 30 to 120 minutes
- Include currently happening events in upcoming meetings API
- Create shared time utility functions (formatDateTime, formatCountdown, formatStartedAgo)
- Improve ongoing meetings UI logic with proper time detection
- Fix backend code organization and remove excessive documentation

UI/UX Improvements:
- Restructure room page layout using MinimalHeader pattern
- Remove borders from header and footer elements
- Change button text from "Leave Meeting" to "Leave Room"
- Remove "Back to Reflector" footer for cleaner design
- Extract WaitPageClient component for better separation

Backend Changes:
- calendar_events.py: Fix import organization and extend timing window
- rooms.py: Update API default from 30 to 120 minutes
- Enhanced test coverage for ongoing meeting scenarios

Frontend Changes:
- MinimalHeader: Add onLeave prop for custom navigation
- MeetingSelection: Complete layout restructure with shared utilities
- timeUtils: New shared utility file for consistent time formatting

🤖 Generated with [Claude Code](https://claude.ai/code)

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

server/tests/test_room_ics_api.py

@@ -357,8 +357,9 @@ async def test_list_upcoming_meetings(authenticated_client):
     response = await client.get(f"/rooms/{room.name}/meetings/upcoming")
     assert response.status_code == 200
     data = response.json()
-    assert len(data) == 1
+    assert len(data) == 2
     assert data[0]["title"] == "Soon"
+    assert data[1]["title"] == "Later"
 
     response = await client.get(
         f"/rooms/{room.name}/meetings/upcoming", params={"minutes_ahead": 180}