fix(ui): stop the owner filter selection overlapping its row label (#…

fix(ui): stop the owner filter selection overlapping its row label (#141405)

The sessions Filter & sort menu drew the selected owner's avatar and name over the Specific owner label. The slotted selection rail inherited flex-shrink 0 from the keycap shortcut idiom inside Web Awesome's fixed-size, end-justified details part, so a rail wider than its column spilled leftward across the label. Give the label part its own capped width, let the details part flex, let the rail shrink, and offset Web Awesome's forced slotted start margin so the row keeps its 8px gutter. The keyboard e2e test now selects a long owner name and asserts the label stays unclipped and clear of the rail.