fix(views): apply the starred default view on first resolve, for feed AND plex (S2)

The feed applied its starred default via a localStorage mirror
(LS.defaultViewFilters) written by SavedViewsProvider and read by
FeedFiltersProvider on load. That raced the login effect: on a genuinely
fresh browser (no LS.filters and no mirror yet) the feed could seed
DEFAULT_FILTERS and never re-apply the default until a reload. Plex had no
default-application at all.

Replace the mirror with a single path: SavedViewsProvider applies the
starred default via cfg.setFilters on the views query's FIRST resolve, but
only into a genuinely fresh module (no stored filters for the account, and
— feed only — no URL filter override). Applying persists it, so it happens
once and the last-view-wins path takes over, matching the documented
storage semantics. Because it runs off cfg.setFilters it delivers the Plex
port for free. Extract pickDefaultToSeed (pure, unit-tested) and cover the
first-resolve/stored/no-default cases for both modules in a provider test.

Removes the now-dead LS.defaultViewFilters key and its mirror read.

frontend/src/lib/savedViews.ts

@@ -10,3 +10,18 @@ export function preferSticky<T extends { id: number }>(
 ): T | null {
   return matches.find((v) => v.id === stickyId) ?? matches[0] ?? null;
 }
+
+/** The starred default view to seed a module's filters with on first load, or null to leave them.
+ *  Seeds ONLY when the module is a genuinely fresh start (`canSeed`: no stored filters for this
+ *  account and — feed only — no URL filter override); otherwise the last-session/URL/manual filters
+ *  win, exactly as they do after any edit. First `is_default` wins if somehow several are flagged, so
+ *  the choice is deterministic. This is the single default-application path for BOTH the feed and Plex
+ *  (SavedViewsProvider drives it on the views query's first resolve) — it replaced the feed-only
+ *  localStorage mirror that raced the login effect and left Plex with no default at all. */
+export function pickDefaultToSeed<T extends { is_default: boolean }>(
+  views: T[],
+  canSeed: boolean,
+): T | null {
+  if (!canSeed) return null;
+  return views.find((v) => v.is_default) ?? null;
+}