style(frontend): Prettier config + one-time repo-wide format pass

Prettier 3 (pinned), printWidth 100, double quotes — chosen to match the existing
hand-formatting and minimise reflow. This commit is ONLY the mechanical format pass
(`prettier --write`) plus the config/ignore/scripts, isolated so it never pollutes a
feature diff. Verified behaviour-neutral: typecheck, eslint (0 errors), and vitest
all green before and after. See .git-blame-ignore-revs — `git blame` skips this sha.

frontend/src/lib/plexDetailUi.tsx

@@ -12,7 +12,8 @@ import { api } from "./api";
 
 export function useDetailPrefs() {
   const qc = useQueryClient();
-  const prefs = (qc.getQueryData<{ preferences?: Record<string, unknown> }>(["me"])?.preferences ?? {}) as {
+  const prefs = (qc.getQueryData<{ preferences?: Record<string, unknown> }>(["me"])?.preferences ??
+    {}) as {
     plexInfoArtBg?: boolean;
     plexInfoCast?: boolean;
     plexInfoRelated?: boolean;
@@ -65,7 +66,11 @@ export function Filterable({
 }) {
   if (!onClick) return <span className={className}>{children}</span>;
   return (
-    <button onClick={onClick} title={title} className={`${className ?? ""} cursor-pointer hover:text-accent transition`}>
+    <button
+      onClick={onClick}
+      title={title}
+      className={`${className ?? ""} cursor-pointer hover:text-accent transition`}
+    >
       {children}
     </button>
   );
@@ -145,9 +150,15 @@ export function DetailCustomizeMenu({
           style={{ background: "color-mix(in srgb, var(--surface) 58%, transparent)" }}
         >
           <PrefToggle label={t("plex.info.prefArtBg")} on={artBg} onClick={onToggleArtBg} />
-          {hasCast && <PrefToggle label={t("plex.info.prefCast")} on={showCast} onClick={onToggleCast} />}
+          {hasCast && (
+            <PrefToggle label={t("plex.info.prefCast")} on={showCast} onClick={onToggleCast} />
+          )}
           {hasRelated && onToggleRelated && (
-            <PrefToggle label={t("plex.info.prefRelated")} on={showRelated ?? true} onClick={onToggleRelated} />
+            <PrefToggle
+              label={t("plex.info.prefRelated")}
+              on={showRelated ?? true}
+              onClick={onToggleRelated}
+            />
           )}
           {extra}
         </div>
@@ -156,15 +167,27 @@ export function DetailCustomizeMenu({
   );
 }
 
-export function PrefToggle({ label, on, onClick }: { label: string; on: boolean; onClick: () => void }) {
+export function PrefToggle({
+  label,
+  on,
+  onClick,
+}: {
+  label: string;
+  on: boolean;
+  onClick: () => void;
+}) {
   return (
     <button
       onClick={onClick}
       className="flex w-full items-center justify-between rounded-lg px-2 py-1.5 text-left hover:bg-surface"
     >
       <span>{label}</span>
-      <span className={`relative h-4 w-7 rounded-full transition ${on ? "bg-accent" : "bg-border"}`}>
-        <span className={`absolute top-0.5 h-3 w-3 rounded-full bg-white transition-all ${on ? "left-3.5" : "left-0.5"}`} />
+      <span
+        className={`relative h-4 w-7 rounded-full transition ${on ? "bg-accent" : "bg-border"}`}
+      >
+        <span
+          className={`absolute top-0.5 h-3 w-3 rounded-full bg-white transition-all ${on ? "left-3.5" : "left-0.5"}`}
+        />
       </span>
     </button>
   );