dash: the live decisions feed is silent to screen readers

`#pending-list` already carries `aria-live="polite"` (`src/doberman/dash/app.py:272`), so a screen reader announces new pending approvals. The `Recent decisions` list right under it, `` (`:275`), has no `aria-live`, so decisions streamed in over SSE are never announced. (#260 is about the tkinter dialog, a different surface; this one is the web dashboard.) **What to do** 1. Add `aria-live="polite"` to the `` tag, mirroring `#pending-list`. 2. Test in `tests/unit/test_dash_polish.py`: the served shell contains `id="feed" aria-live="polite"` (or the attribute in whichever order you write it). One attribute. Heads-up: #401 and #415 are in flight against `dash/app.py`; branch from a fresh `main`.