Audit Sessions filter row lead-task reason

Found while checking Task 8086 at 1280px. 1. Desktop filter row wraps to two lines at 1280px: Transcript and End reason size to their longest option (the "Stale (never started, over …)" label), so Node and Search land on a second line. Cap those two selects (e.g. `maxWidth`) so the row fits one line at ≥1280px. 2. With "+N" open on desktop, the lead task's runner reason sits on a line beneath it while each other task's reason sits beside it in the Cause/Node columns; place the lead's reason the same way so the list reads uniformly. 3. The desktop Search placeholder truncates ("name, session id, bra…") whenever the row is tight; shorten it or give the field a larger floor. Out of scope: the phone layout (fixed in 8086), the grouping rule, liveness and transcript states. Done means: - Screenshots of Audit › Sessions at 1280px showing one filter line and a uniform open "+N" list.

Audit › Sessions at 1280px: the filter row fits one line (Transcript/End reason capped on desktop), every reason in an open "+N" list sits in the Cause column, and the Search hint shows whole. Phone layout unchanged. Visual check done at 1280 and 390px. Quick gate green, review approved; PR #6309 queued to the lane. Filed draft 8107.