Fix task board polish issues

Itemized suggestions from photographing the task board (/tasks) on prod during docs-writer Task 8138: 1. Picking an option in Filter & view (e.g. State → Draft) leaves the popover and its invisible backdrop open, so the next click on the board (e.g. "☑ Select all") is swallowed; close the menu, or let the click pass through, once a single-choice option is picked. 2. On phones, a held row's grey reason line reads "Waiting. Node runner limit (6/6): slot 1 held by #6234, slot 2 held by …" and is cut off; show a short reason ("Waiting for a free runner slot") and keep the slot list in the hover/⋯ item. 3. The Focus button's tooltip says "hide finished and archived tasks", but Focus also hides queued subtasks; make the tooltip match what it does. 4. Section headers lost their per-kind breakdown (e.g. "2 questions, 1 failed"); consider restoring a short breakdown on Stopped so a glance tells failed from paused. Out of scope: the docs pages (apps/docs) — updated separately; any change to task states or filtering semantics. Done means: each item is either fixed (rendered on a live stack at desktop and ≤480px, screenshot attached) or recorded as declined with a one-line reason; ./dc check quick green.

Fixed all 4 board items. Filter & view picks now close the panel; the phone hold line is short; the Focus tooltip is corrected; Stopped shows its failed/paused split. Checked live at desktop and 390px. Quick gate green. PR #6341 merged (ba6d230). Its deploy was superseded. Follow-up draft #8196.