feat(feed): pick the feed's view from its own toolbar

The view mode moves out of Settings into a switcher next to sort, on the
feed and channel pages alike. It leaves the Settings prefs draft for its
own eager save: a toolbar click must not mark that page dirty and trip
its leave-page guard.

lib/feedView.ts owns the vocabulary and maps the old grid/list prefs
forward on read, so nobody's saved choice is lost.

frontend/src/components/SettingsPanel.tsx

@@ -20,8 +20,6 @@ export type PrefsSaveState = SaveState;
 export interface PrefsController {
   theme: ThemePrefs;
   setTheme: (t: ThemePrefs) => void;
-  view: "grid" | "list";
-  setView: (v: "grid" | "list") => void;
   perf: boolean;
   setPerf: (v: boolean) => void;
   hints: boolean;
@@ -128,7 +126,7 @@ function Appearance({ prefs }: { prefs: PrefsController }) {
   const { t } = useTranslation();
   // Controlled by App's prefs draft: each change applies locally for preview but is only
   // persisted on an explicit Save (handled by the panel's Save/Discard bar).
-  const { theme, setTheme, view, setView, perf, setPerf, hints, setHints } = prefs;
+  const { theme, setTheme, perf, setPerf, hints, setHints } = prefs;
 
   return (
     <>
@@ -186,13 +184,6 @@ function Appearance({ prefs }: { prefs: PrefsController }) {
             />
           </div>
         )}
-        <SettingRow label={t("settings.appearance.listView")} hint={t("settings.appearance.listViewHint")}>
-          <Switch
-            label={t("settings.appearance.listView")}
-            checked={view === "list"}
-            onChange={(v) => setView(v ? "list" : "grid")}
-          />
-        </SettingRow>
         <SettingRow
           label={t("settings.appearance.performanceMode")}
           hint={t("settings.appearance.performanceModeHint")}