test: add tests for UI store

[d3vobed]

Adds comprehensive tests for the UI store:

• Initial state verification
• Modal actions: openModal, closeModal, setModalData (with merge)
• Sidebar actions: toggleSidebar, setSidebarOpen, setSidebarView
• Toast actions: addToast (with custom duration), removeToast, clearToasts
• Loading actions: setGlobalLoading with/without message
• Selection actions: setSelectedAsset, setSelectedBridge, setSelectedTimeRange
• Insights tray: openInsightsTray, closeInsightsTray
• View actions: setIsMobileView, setIsTouchDevice
• ResetUI: full state reset to initial values
• Selectors: all exported selectors
• Edge cases: closing modal when none is open, removing non-existent toast, toast auto-id format, tray close preserves asset

Follows existing store test conventions from notificationStore.test.ts.

Closes #763

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