* feat: make the Files explorer tree pane resizable
Operators can drag the Files tab divider to read long or deeply nested names. The width is remembered in this browser; names that still overflow scroll horizontally.
* fix: keep Files tree resize from leaking cursor or stealing row clicks
Unmount and lost-pointer-capture now clear the drag gesture. The stored width stays a preference while layout clamps to the explorer size, and the hit target only expands into the viewer so full-row context menus still work.
* fix: persist last live Files pane width on pointercancel
Cancel events can report clientX 0, which was clamping the tree to 160px and writing that to storage. Commit the last tracked width instead, same as lostpointercapture.
Anso
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