Fix the Settings pane clipping, align the Files pane, and show a pointer over the new chrome buttons

[jonnilundy]

Found by running PR #3 in the real app.

Fixed

• Settings > Files was clipped on the right (Change…, the remove button and Restore Defaults cut off). Two causes: the path label had a fixed width that made the pane wider than the window, and the window never followed the pane after a location was added. The path label now takes the leftover space and truncates in the middle (the tooltip keeps the full path). The window grows and shrinks to fit the pane.
• Alignment: the marker, nickname, Add Location… and the File associations box share one left edge. The label lines up with the first row's baseline. The right edges line up. Rows are even. The grid matches the other panes.
• Cursor: the palette destination chip, the Overflow and Alternatives panel buttons, the M↓ toggle and the file name bar now show the pointing hand instead of the text cursor. The cause: the page's text view registers an I-beam under any view that registers no cursor of its own. One small helper, PointerCursor.swift.

Verified here

• swift build passes.
• Offscreen renders of the Files pane before and after (light and dark; empty, one long path, three, a long nickname). The before render reproduces the clipping from the screenshot. After: nothing clipped in all 8 cases.
• 94 UI-side tests pass through an XCTest stand-in, including new layout tests and cursor registration tests.

Not verified

• Real hover: cursor rects cannot be tested offscreen. The tests check what each view registers, not what AppKit shows.
• Real swift test.

Not fixed (follow-up)

• The Alternatives panel body and the Overflow panel outside its text probably still show the text cursor over non-text areas.

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