feat(series): land on the current episode, not season 1 (UR-062, UR-063, UR-064)

Opening a series dumped the viewer at the top of season 1, and its Play
button played nothing at all: it resolved `$libraryItems[0]` — the first
*season* by SortName — and navigated to `/player/<seasonId>`, which the
player route bounced straight back to `/library/<seasonId>`.

The backend could already answer "where is this viewer in this show":
`repository_get_next_up_episodes` has accepted a `series_id` since it was
written and no caller had ever passed one.

Backend (DR-101, DR-106)
- `repository/series_progress.rs`: `pick_current_episode` — in progress,
  else Next Up, else first unwatched, else the premiere. The third rung is
  the offline path, where Next Up is always empty. `sort_series_order` puts
  specials (season 0) after the numbered seasons.
- `repository_get_series_episodes` takes over the season fan-out and the
  flat-series fallback, which were domain knowledge living in the frontend.
- `clear_watch_history` maps to Jellyfin's mark-unplayed (recursive over a
  container, also zeroes resume). Offline it refuses rather than diverging
  state the next sync would undo.

Frontend (DR-102, DR-103, DR-104, DR-107)
- Seasons collapse; only the current one is expanded, and the current
  episode is badged and scrolled into view.
- Hero button reads `Resume S2E4` / `Play S1E1` and opens that episode's
  focus view, where Play commits (ux-flows §5B.5).
- Seasons are no longer a destination: `/library/<seasonId>` redirects to
  `/library/<seriesId>#season-N`, and every inbound link follows.
- The "More Episodes" strip spans the whole series, so a season finale
  offers the next premiere instead of dead-ending (§5B.2).
- Clear-history buttons on the series hero and each season header.

Routes (DR-105)
- `/library/tv` and `/library/movies` absorb their all-titles and genres
  pages as `?view=` tabs; the four legacy routes redirect. 6 video routes
  become 2, and `/library/shows/genres` stops being the odd one out.

Logic extracted to `seriesNavigation.ts`, `episodeStrip.ts` and
`libraryView.ts` so it is unit-tested rather than buried in components.
Spec: docs/specs/series-current-episode-navigation.md

src/lib/utils/libraryView.test.ts

@@ -0,0 +1,49 @@
+import { describe, it, expect } from "vitest";
+import {
+  resolveLibraryView,
+  libraryViewUrl,
+  LIBRARY_VIEWS,
+  DEFAULT_LIBRARY_VIEW,
+} from "./libraryView";
+
+describe("resolveLibraryView", () => {
+  it("resolves each known view", () => {
+    for (const view of LIBRARY_VIEWS) {
+      expect(resolveLibraryView(view)).toBe(view);
+    }
+  });
+
+  it("defaults to browse when the param is absent", () => {
+    expect(resolveLibraryView(null)).toBe("browse");
+    expect(resolveLibraryView(undefined)).toBe("browse");
+  });
+
+  it("falls back to the default rather than rendering nothing for junk", () => {
+    expect(resolveLibraryView("shows")).toBe(DEFAULT_LIBRARY_VIEW);
+    expect(resolveLibraryView("")).toBe(DEFAULT_LIBRARY_VIEW);
+  });
+
+  it("tolerates case and surrounding whitespace", () => {
+    expect(resolveLibraryView("Genres")).toBe("genres");
+    expect(resolveLibraryView(" all ")).toBe("all");
+  });
+});
+
+describe("libraryViewUrl", () => {
+  it("omits the param for the default view so the landing URL stays clean", () => {
+    expect(libraryViewUrl("/library/tv", "browse")).toBe("/library/tv");
+  });
+
+  it("names the non-default views", () => {
+    expect(libraryViewUrl("/library/tv", "all")).toBe("/library/tv?view=all");
+    expect(libraryViewUrl("/library/movies", "genres")).toBe("/library/movies?view=genres");
+  });
+
+  it("round-trips through resolveLibraryView", () => {
+    for (const view of LIBRARY_VIEWS) {
+      const url = libraryViewUrl("/library/tv", view);
+      const param = new URL(url, "http://x").searchParams.get("view");
+      expect(resolveLibraryView(param)).toBe(view);
+    }
+  });
+});

src/lib/utils/libraryView.ts

@@ -0,0 +1,36 @@
+// Which section of a video library page is showing.
+//
+// Browse / All / Genres used to be three routes per library, named
+// inconsistently across the two libraries (`/library/tv/shows` vs
+// `/library/movies/all`; `/library/shows/genres` vs `/library/movies/genres`).
+// They are now one route with tabs, and this is the pure `?view=` ↔ tab
+// mapping.
+//
+// TRACES: UR-063 | DR-105
+export type LibraryView = "browse" | "all" | "genres";
+
+/** Tab order, left to right. `browse` leads because it is the landing view. */
+export const LIBRARY_VIEWS: readonly LibraryView[] = ["browse", "all", "genres"];
+
+/** The view a page shows when `?view=` is absent or unrecognised. */
+export const DEFAULT_LIBRARY_VIEW: LibraryView = "browse";
+
+/**
+ * Read a `?view=` value. Anything unknown — a typo, a stale bookmark, a
+ * removed tab — lands on the default rather than rendering nothing.
+ */
+export function resolveLibraryView(value: string | null | undefined): LibraryView {
+  if (value == null) return DEFAULT_LIBRARY_VIEW;
+  const normalized = value.trim().toLowerCase();
+  return (LIBRARY_VIEWS as readonly string[]).includes(normalized)
+    ? (normalized as LibraryView)
+    : DEFAULT_LIBRARY_VIEW;
+}
+
+/**
+ * URL for a tab. The default view omits the param, so the landing URL stays
+ * `/library/tv` — the same convention `searchRouteUrl` uses for the `all` scope.
+ */
+export function libraryViewUrl(basePath: string, view: LibraryView): string {
+  return view === DEFAULT_LIBRARY_VIEW ? basePath : `${basePath}?view=${view}`;
+}

src/lib/utils/searchScope.ts

@@ -42,7 +42,9 @@ export function resolveSearchScope(pathname: string): SearchScope {
   if (path === "/library/music" || path.startsWith("/library/music/")) return "music";
   if (path === "/library/movies" || path.startsWith("/library/movies/")) return "movies";
   if (path === "/library/tv" || path.startsWith("/library/tv/")) return "tv";
-  // `/library/shows/genres` is the TV genre route despite the differing segment.
+  // `/library/shows/*` is a legacy TV route that now redirects into
+  // `/library/tv?view=genres` (DR-105). Kept so a search typed on the URL
+  // before the redirect lands still scopes to TV.
   if (path === "/library/shows" || path.startsWith("/library/shows/")) return "tv";
 
   return "all";