refactor: component files export only components; lint fails on a warning

The 43 react-refresh/only-export-components warnings the gate let through meant an edit to a
provider (or AnchoredPopover, Toaster, plexDetailUi, …) could not be hot-swapped: Fast Refresh
reloads a module that also exports hooks or helpers.

- Each provider's contexts, the types its hooks return and the hooks themselves live in a sibling
  context module (navigationContext.ts, channelsContext.ts, …); the provider file keeps the
  component. loadAccountFilters moved next to the feed filters' defaults (feedFiltersInit.ts),
  following navigationInit/playlistsInit.
- Helpers that sat in component files have their own modules: welcomeMode, downloadTitle,
  plexPlayable, channelSync, ui/anchoredPopoverHooks, ui/pageToolbarSlot, ui/pagerContent,
  ui/toastLevels, ui/overlayOrder, ui/tableAlign, lib/plexDetail; the cells of the channel columns
  and the registry's page wrappers are components files of their own (channelCells, modulePages).
- usePersistedTab, an alias of useAccountPersistedState, is gone; its callers use the original.

npm run lint is now eslint --max-warnings 0, so a warning fails the gate like an error does.

frontend/src/components/SavedViewsProvider.tsx

@@ -1,20 +1,10 @@
-import {
-  createContext,
-  useContext,
-  useEffect,
-  useMemo,
-  useRef,
-  useState,
-  type ReactNode,
-} from "react";
+import { useEffect, useMemo, useRef, useState, type ReactNode } from "react";
 import { useTranslation } from "react-i18next";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { qk } from "../lib/queryKeys";
 import {
   api,
   coercePlexFilters,
-  coerceTagModes,
-  coerceUntagged,
   getActiveAccount,
   plexFiltersSignature,
   type FeedFilters,
@@ -25,27 +15,23 @@ import { filtersToParams, hasFilterParams } from "../lib/urlState";
 import { pickDefaultToSeed, preferSticky } from "../lib/savedViews";
 import { notifyActionError } from "../lib/actionErrors";
 import { accountKey, LS } from "../lib/storage";
-import { useConfirm } from "./ConfirmProvider";
-import { useNavigation } from "./NavigationProvider";
-import { useFeedFilters, useFeedFiltersActions } from "./FeedFiltersProvider";
-import { usePlex, usePlexActions } from "./PlexProvider";
+import { useConfirm } from "./confirmContext";
+import { useNavigation } from "./navigationContext";
+import { useFeedFilters, useFeedFiltersActions } from "./feedFiltersContext";
+import { usePlex, usePlexActions } from "./plexContext";
+import {
+  asFilters,
+  SavedViewsCtx,
+  type SavedViewsContext,
+  type ViewSource,
+} from "./savedViewsContext";
 
 // Saved "smart views" now serve TWO modules — the feed and Plex — keyed by `source`. This one provider
 // switches which module it operates on by the active page (both filter providers are global, so it can
 // read either), so the shared UI (popover / modal / chip) works on the feed page against feed views and
 // on the plex page against plex views without a second provider or an App-layout change.
-
-// A saved view's `filters` is an opaque JSON blob from the DB; coerce it to the module's shape before it
-// reaches app state or a serializer (an older build's dropped field just falls away — NOT a migration).
-export const asFilters = (raw: FeedFilters): FeedFilters => ({
-  ...raw,
-  tags: raw.tags ?? [],
-  channelIds: raw.channelIds ?? [],
-  tagModes: coerceTagModes(raw),
-  untagged: coerceUntagged(raw),
-});
-
-type ViewSource = "feed" | "plex";
+//
+// The context, its value type and the hook live in savedViewsContext.ts.
 
 // The per-source wiring the generic logic runs on: the live filters, how to apply a view's, a stable
 // signature for matching, coercion, and what to strip before saving (the feed's transient shuffle seed).
@@ -87,33 +73,6 @@ function plexCanSeedDefault(): boolean {
   return !storedFiltersPresent(LS.plexFilters);
 }
 
-export interface SavedViewsContext {
-  /** Which module these views belong to — the shared UI branches its filter-describer on it. */
-  source: ViewSource;
-  views: SavedView[];
-  loading: boolean;
-  activeViewId: number | null;
-  displayView: SavedView | null;
-  isDirty: boolean;
-  modalOpen: boolean;
-  openModal: () => void;
-  closeModal: () => void;
-  apply: (v: SavedView) => void;
-  clearActive: () => void;
-  create: (name: string) => Promise<boolean>;
-  rename: (id: number, name: string) => Promise<boolean>;
-  /** Overwrite a view's captured filters (used by the modal's removable chips). */
-  updateFilters: (id: number, filters: Record<string, unknown>) => Promise<boolean>;
-  /** Save the module's CURRENTLY-applied filters into a view (the live→stored inverse of `apply`);
-   *  resolves to the saved snapshot on success (so the caller can resync its editor) or null. */
-  saveCurrent: (id: number) => Promise<Record<string, unknown> | null>;
-  toggleDefault: (v: SavedView) => Promise<void>;
-  remove: (v: SavedView) => Promise<boolean>;
-  reorder: (nextIds: number[]) => Promise<void>;
-}
-
-const Ctx = createContext<SavedViewsContext | null>(null);
-
 export function SavedViewsProvider({ children }: { children: ReactNode }) {
   const { t } = useTranslation();
   const qc = useQueryClient();
@@ -295,11 +254,5 @@ export function SavedViewsProvider({ children }: { children: ReactNode }) {
     },
   };
 
-  return <Ctx.Provider value={value}>{children}</Ctx.Provider>;
-}
-
-export function useSavedViews(): SavedViewsContext {
-  const ctx = useContext(Ctx);
-  if (!ctx) throw new Error("useSavedViews must be used within a SavedViewsProvider");
-  return ctx;
+  return <SavedViewsCtx.Provider value={value}>{children}</SavedViewsCtx.Provider>;
 }