Fix ResizeObserver memory leak in matrix view

[Copilot]

The ResizeObserver created in drawComparisonMatrix() was never disconnected when switching views or recreating the matrix, causing observers to accumulate in memory.

Changes

Store enhancement (comparison-renderer-store.js):

• Added resizeObserver field and methods: setResizeObserver(), getResizeObserver(), disconnectResizeObserver()
• Updated clear() to automatically disconnect observer

Cleanup integration (comparison-renderer.js):

• Store observer reference when creating matrix view
• Disconnect observer before clearing container in drawComparisonTree() and drawInlineFocusedComparison()

Cleanup scenarios

Observer is now disconnected when:

• Switching between view modes (matrix → tree, matrix → focused)
• Recreating matrix view (via matrixStore.clear())
• Replacing existing observer (auto-disconnect in setResizeObserver())

// In drawComparisonMatrix
const resizeObserver = new ResizeObserver(() => { /* ... */ });
resizeObserver.observe(matrixContainer);
matrixStore.setResizeObserver(resizeObserver);  // Stored for cleanup

// In view switching functions
cleanupStore.disconnectResizeObserver();  // Explicit cleanup
vizContainer.innerHTML = '';

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