Use a scroll view for agents in the tray window

When there are many agents, the agent view can overflow. We should put the agents inside a scroll view and set a max height before scrolling kicks in.

Parity with macOS, which already has this functionality: https://github.com/coder/coder-desktop-macos/pull/197

Start by locating the tray window and its agent view in the Windows application, then compare the requested behavior with the linked macOS pull request. Add scrolling for overflowing agents with a maximum view height, and verify the tray window remains usable when many agents are present.

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