Make team identity window-owned

[IsaiahWitzke]

Description

Moves team selection out of the UserWorkspaces singleton's mutable WindowId → team_uid map and makes it immutable window-owned state.

• Introduces WindowTeam, initialized once per window.
• Carries the same team identity through RootView, Workspace, restoration, inherited windows, detached tabs, and explicit team-switch windows.
• Keeps UserWorkspaces responsible for resolving the selected UID to live team/workspace metadata.
• Removes metadata-refresh reconciliation that could retarget an existing window.
• Preserves lightweight test-only team overrides for fixtures that do not construct a full workspace window.

This is a direction-review draft related to the broader X-Warp-Team-Uid work in https://github.com/warpdotdev/warp-server/pull/14108. It does not yet attach the header to MAA requests.

Linked Issue

No linked issue yet; this draft is intended to review the client ownership model before expanding the transport/server work.

• The linked issue is labeled ready-to-spec or ready-to-implement.
• Where appropriate, screenshots or a short video of the implementation are included below (especially for user-visible or UI changes).

Testing

Not run for this direction-review draft, per request.

• I have manually tested my changes locally with ./script/run

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-NONE

[IsaiahWitzke]

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