refactor(fe): eliminate every explicit any; enforce no-explicit-any (R7 S3a·4)

Removes all 13 remaining `any`s and flips the ESLint rule from off to error so
new ones can't creep back:
- api.ts prefs/data JSON bags: Record<string, any> -> Record<string, unknown>,
  narrowed at consumers (App language guard; NotificationsPanel shapes the
  notification `data` per type behind its existing typeof guards)
- catch (e: any) -> catch (e) + `e instanceof HttpError` narrowing
  (SettingsPanel, SetupWizard, PlexPlayer)
- the YouTube IFrame API boundary: new lib/youtube.ts types (YTPlayer/
  YTPlayerEvent/YTNamespace + a Window augmentation) replace the 6 player anys;
  tsc surfaced the exact method surface to declare
- NotificationsPanel `t` props: any-options -> i18next TFunction

Gate green: typecheck (app+node+e2e), eslint 0 errors (rule now enforced),
prettier, 74 vitest.

frontend/src/components/NotificationsPanel.tsx

@@ -1,5 +1,6 @@
 import { useEffect, useSyncExternalStore } from "react";
 import { useTranslation } from "react-i18next";
+import type { TFunction } from "i18next";
 import { useMutation, useQueryClient } from "@tanstack/react-query";
 import { qk } from "../lib/queryKeys";
 import {
@@ -223,7 +224,7 @@ function NotificationRow({
   onOpenScheduler,
 }: {
   n: AppNotification;
-  t: (k: string, o?: any) => string;
+  t: TFunction;
   onRead: () => void;
   onDismiss: () => void;
   onOpenScheduler: () => void;
@@ -239,15 +240,18 @@ function NotificationRow({
   let title = n.title;
   let body = n.body;
   if (isMaintenance) {
+    // Guarded above (typeof count === "number"); shape the JSON `data` bag for typed access.
+    const d = n.data as { count: number };
     title = t("inbox.maintenance.title");
-    body = t("inbox.maintenance.body", { count: n.data!.count });
+    body = t("inbox.maintenance.body", { count: d.count });
   } else if (isScheduler) {
     // "<Job label> finished/failed", with the raw result summary as the (technical) body.
-    const job = t(`scheduler.jobs.${n.data!.job_id}`, n.data!.job_id);
-    title = t(n.data!.status === "error" ? "inbox.jobDone.titleError" : "inbox.jobDone.titleOk", {
+    const d = n.data as { job_id: string; status?: string; summary?: string };
+    const job = t(`scheduler.jobs.${d.job_id}`, d.job_id);
+    title = t(d.status === "error" ? "inbox.jobDone.titleError" : "inbox.jobDone.titleOk", {
       job,
     });
-    body = n.data!.summary || n.body;
+    body = d.summary || n.body;
   }
   return (
     <div
@@ -320,7 +324,7 @@ function ClientActivityRow({
   onRemove,
 }: {
   n: ClientNotif;
-  t: (k: string, o?: any) => string;
+  t: TFunction;
   onFind: (meta: VideoHiddenMeta | VideoWatchedMeta) => void;
   onRevert: (meta: VideoHiddenMeta | VideoWatchedMeta) => void;
   onFocusChannel: (name: string) => void;

frontend/src/components/PlayerModal.tsx

@@ -30,6 +30,7 @@ import AddToPlaylist from "./AddToPlaylist";
 import { modalCount } from "./Modal";
 import DownloadButton from "./DownloadButton";
 import { api, type Video, type VideoStatus } from "../lib/api";
+import type { YTNamespace, YTPlayer, YTPlayerEvent } from "../lib/youtube";
 import {
   channelYouTubeUrl,
   formatDate,
@@ -82,16 +83,17 @@ function canScrollBy(el: HTMLElement | null, dir: -1 | 1): boolean {
 }
 
 // --- IFrame Player API loader (singleton) ---
-let apiPromise: Promise<any> | null = null;
-function loadYouTubeApi(): Promise<any> {
+let apiPromise: Promise<YTNamespace> | null = null;
+function loadYouTubeApi(): Promise<YTNamespace> {
   if (apiPromise) return apiPromise;
-  apiPromise = new Promise((resolve) => {
-    const w = window as any;
+  apiPromise = new Promise<YTNamespace>((resolve) => {
+    const w = window;
     if (w.YT && w.YT.Player) return resolve(w.YT);
     const prev = w.onYouTubeIframeAPIReady;
     w.onYouTubeIframeAPIReady = () => {
       if (typeof prev === "function") prev();
-      resolve(w.YT);
+      // The API-ready callback only fires once the script has installed window.YT.
+      resolve(w.YT!);
     };
     const tag = document.createElement("script");
     tag.src = "https://www.youtube.com/iframe_api";
@@ -158,7 +160,7 @@ export default function PlayerModal({
   const resumeAt =
     startAt != null && active.id === video.id ? startAt : active.position_seconds || 0;
   const mountRef = useRef<HTMLDivElement | null>(null);
-  const playerRef = useRef<any>(null);
+  const playerRef = useRef<YTPlayer | null>(null);
   const autoMarkedRef = useRef(false);
   // Bound consecutive unplayable items so an auto-advancing queue (esp. loop=all) can't spin over a
   // run of dead videos — after the cap we stop on the error overlay instead of skipping forever.
@@ -706,7 +708,7 @@ export default function PlayerModal({
             focusModal();
             applyVolume(volumeRef.current, false);
           },
-          onStateChange: (e: any) => {
+          onStateChange: (e: YTPlayerEvent) => {
             // 1 === playing → sync the navigated-to video's title/author for display.
             if (e?.data === 1) {
               errorStreakRef.current = 0; // a successful play breaks any unplayable run
@@ -725,7 +727,7 @@ export default function PlayerModal({
           },
           // The embed couldn't play this video (embedding disabled, removed, private…).
           // Surface our own message + an "Open on YouTube" escape hatch.
-          onError: (e: any) => {
+          onError: (e: YTPlayerEvent) => {
             setPlayerError(typeof e?.data === "number" ? e.data : -1);
             // The IFrame API fires onError (not 'ended') for an unplayable item, so advanceOnEnd()
             // never runs and an auto-advancing queue would freeze here. Skip forward instead — but

frontend/src/components/PlexPlayer.tsx

@@ -34,7 +34,7 @@ import {
   VolumeX,
   X,
 } from "lucide-react";
-import { api, type PlexMarker } from "../lib/api";
+import { api, HttpError, type PlexMarker } from "../lib/api";
 import { formatDuration } from "../lib/format";
 import {
   exitFullscreen,
@@ -314,14 +314,15 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
         // selected client-side after the manifest loads.
         const m = multiAudioRef.current;
         sess = await api.plexSession(id, startAt, m ? null : audioRef.current, aoffRef.current, m);
-      } catch (e: any) {
+      } catch (e) {
         // Surface WHY playback can't start instead of an eternal spinner. 404 = the physical file
         // isn't reachable (missing media bind-mount or a wrong plex_path_map); 501 = the codec
         // needs full transcoding (a later phase).
+        const status = e instanceof HttpError ? e.status : undefined;
         setLoadError(
-          e?.status === 501
+          status === 501
             ? tRef.current("plex.player.errTranscode")
-            : e?.status === 404
+            : status === 404
               ? tRef.current("plex.player.errNotFound")
               : tRef.current("plex.player.errGeneric"),
         );

frontend/src/components/SettingsPanel.tsx

@@ -4,7 +4,7 @@ import { useTranslation } from "react-i18next";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { Bell, Check, Loader2, Monitor, RefreshCw, Trash2, User } from "lucide-react";
 import { SCHEMES, type Scheme, type ThemePrefs } from "../lib/theme";
-import { api, type Me } from "../lib/api";
+import { api, HttpError, type Me } from "../lib/api";
 import { LS, useAccountPersistedState } from "../lib/storage";
 import Avatar from "./Avatar";
 import { notify, type NotifSettings } from "../lib/notifications";
@@ -393,8 +393,10 @@ function SignInMethods({ me }: { me: Me }) {
         level: "success",
         message: t("settings.account.password.saved", { email: me.email }),
       });
-    } catch (e: any) {
-      setErr(e?.detail ?? t("settings.account.password.failed"));
+    } catch (e) {
+      setErr(
+        (e instanceof HttpError ? e.detail : undefined) ?? t("settings.account.password.failed"),
+      );
     } finally {
       setBusy(false);
     }

frontend/src/components/SetupWizard.tsx

@@ -1,7 +1,7 @@
 import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { Check, ChevronLeft, ChevronRight, Loader2, Send } from "lucide-react";
-import { api } from "../lib/api";
+import { api, HttpError } from "../lib/api";
 import { setLanguage, type LangCode } from "../i18n";
 import LanguageSwitcher from "./LanguageSwitcher";
 
@@ -103,8 +103,8 @@ export default function SetupWizard() {
         return;
       }
       go(1);
-    } catch (e: any) {
-      setError(e?.detail ?? t("setup.genericError"));
+    } catch (e) {
+      setError((e instanceof HttpError ? e.detail : undefined) ?? t("setup.genericError"));
     } finally {
       setBusy(false);
     }