refactor(feed): let the caller decide where the mode's name fits

The xl breakpoint was a fact about the FEED's toolbar, hard-coded into
the switcher that E4's managers are meant to reuse — their rows are far
emptier and would have hidden the label for no reason. It's a prop now,
defaulting to icon-only.

The two views spans collapse into one builder, which also fixes a
regression I'd just added: splitting them put the exact-count tooltip on
the number alone, so hovering the word gave nothing.

frontend/src/components/Feed.tsx

@@ -656,6 +656,9 @@ export default function Feed({
           options={FEED_VIEWS.map((id) => ({ id, label: t("feed.view." + id), icon: VIEW_ICON[id] }))}
           onChange={setView}
           label={t("feed.viewLabel")}
+          // This toolbar is packed — show/content chips, source, count, sort — so the mode's name
+          // only earns its place once the window is wide.
+          labelClassName="hidden xl:inline"
         />
         </div>
       </div>