chore(hygiene): Phase 4 guardrails — noUnusedLocals/Parameters + dead-code sweep

Enable tsconfig noUnusedLocals + noUnusedParameters (permanent guardrail: every tsc/
build now flags re-accumulated dead code). Fixed the 8 violations that surfaced, all
genuine dead code:
- Sidebar: deleted unused SORT_IDS/SHOW_IDS/rollSeed consts + the dead Toggle component
  (+ its now-unused Switch import).
- PlexBrowse: dropped the unused onClearSearch prop (Props + destructure + App call site).
- VideoEditor: dropped the unused map index; notifications: deleted the dead back-compat
  toast(); storage: deleted the unused non-account usePersistedState (+ readJSON import).
- SavedViewsWidget: deleted the dead loadDefaultViewFilters export (App loads the default
  view inline; resolves the last knip unused-export → knip now clean).

Backend: added backend/ruff.toml (ignore E402 — intentional pre-import setup in main.py)
and fixed the 6 E702/E741 style items (_vtt_s_to_ts semicolons, ambiguous `l` loop vars)
so ruff is green. localdev boots; Feed/Plex/sidebar render; 0 console errors.

frontend/src/components/PlexBrowse.tsx

@@ -54,7 +54,6 @@ type Sub =
 
 type Props = {
   q: string;
-  onClearSearch: () => void;
   scope: string; // movie | show | both (unified cross-library scope)
   setScope: (v: string) => void;
   show: string;
@@ -70,7 +69,6 @@ const PAGE = 40;
 
 export default function PlexBrowse({
   q,
-  onClearSearch,
   scope,
   setScope,
   show,

frontend/src/components/SavedViewsWidget.tsx

@@ -20,7 +20,7 @@ import { CSS } from "@dnd-kit/utilities";
 import { api, getActiveAccount, type FeedFilters, type SavedView } from "../lib/api";
 import { filtersToParams, shareUrl } from "../lib/urlState";
 import { notify } from "../lib/notifications";
-import { accountKey, LS, readJSON, writeJSON } from "../lib/storage";
+import { accountKey, LS, writeJSON } from "../lib/storage";
 import { useConfirm } from "./ConfirmProvider";
 
 // Compact, order-independent signature of a filter set (reuses the share serializer, which
@@ -28,14 +28,6 @@ import { useConfirm } from "./ConfirmProvider";
 // saved view that matches the feed's current filters.
 const keyOf = (f: FeedFilters) => filtersToParams(f).toString();
 
-/** The default view's filters, or null. Read synchronously on load (App.loadAccountFilters) from a
- * per-account localStorage mirror the widget keeps in sync — avoids a flash before the query loads.
- * Per-account so one account's default view never seeds another account's feed. */
-export function loadDefaultViewFilters(): FeedFilters | null {
-  const key = accountKey(LS.defaultViewFilters, getActiveAccount());
-  return key ? readJSON<FeedFilters | null>(key, null) : null;
-}
-
 function syncDefaultMirror(views: SavedView[]): void {
   const key = accountKey(LS.defaultViewFilters, getActiveAccount());
   if (!key) return;

frontend/src/components/Sidebar.tsx

@@ -39,29 +39,11 @@ import {
 import { shareUrl } from "../lib/urlState";
 import { notify } from "../lib/notifications";
 import { useDebounced } from "../lib/useDebounced";
-import { Switch } from "./ui/form";
 import TagManager from "./TagManager";
 import SavedViewsWidget from "./SavedViewsWidget";
 import CollapsedFilterRail from "./CollapsedFilterRail";
 
 // Filter ids; display labels resolved at render time via t("sidebar.sort.<id>") etc.
-const SORT_IDS = [
-  "newest",
-  "oldest",
-  "views",
-  "duration_desc",
-  "duration_asc",
-  "title",
-  "subscribers",
-  "priority",
-  "shuffle",
-];
-
-const SHOW_IDS = ["unwatched", "in_progress", "all", "watched", "hidden"];
-
-// Fresh shuffle token for the "surprise me" sort.
-const rollSeed = () => Math.floor(Math.random() * 1_000_000_000);
-
 const DATE_PRESETS: { days: number; key: string }[] = [
   { days: 1, key: "24h" },
   { days: 7, key: "1week" },
@@ -697,19 +679,3 @@ function WidgetCard({
   );
 }
 
-function Toggle({
-  label,
-  checked,
-  onChange,
-}: {
-  label: string;
-  checked: boolean;
-  onChange: (v: boolean) => void;
-}) {
-  return (
-    <label className="flex items-center justify-between py-1 cursor-pointer text-sm">
-      <span>{label}</span>
-      <Switch label={label} checked={checked} onChange={onChange} />
-    </label>
-  );
-}

frontend/src/components/VideoEditor.tsx

@@ -366,7 +366,7 @@ export default function VideoEditor({ job, onClose }: { job: DownloadJob; onClos
               </div>
             )}
             {/* segment tint: dropped = dimmed + hatched */}
-            {segments.map((s, i) => (
+            {segments.map((s) => (
               <div
                 key={s.id}
                 className={clsx(