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/components/library/episodeStrip.test.ts

@@ -1,6 +1,6 @@
 import { describe, it, expect } from "vitest";
 import type { MediaItem } from "$lib/api/types";
-import { isCurrentEpisode, adjacentEpisodes } from "./episodeStrip";
+import { isCurrentEpisode, adjacentEpisodes, compareSeriesOrder, stripCardLabel } from "./episodeStrip";
 
 // Minimal episode factory — only the fields the strip logic reads.
 function ep(
@@ -71,11 +71,41 @@ describe("adjacentEpisodes", () => {
     expect(strip).toContain(current);
   });
 
-  it("restricts to the current season when multiple seasons are present", () => {
+  // ux-flows §5B.2, "Cross-season continuity": the window spans the whole
+  // series in episode order, so it runs past a season boundary rather than
+  // dead-ending at the end of a season.
+  it("runs past the end of a season into the next one", () => {
     const eps = [...season(1, 5), ...season(2, 5)];
-    const current = eps[6]; // S2E2
+    const current = eps[4]; // S1E5 — the season finale
     const strip = adjacentEpisodes(current, eps);
-    expect(strip.every((e) => e.parentIndexNumber === 2)).toBe(true);
+    expect(strip.map((e) => e.id)).toEqual([
+      "s1e2", "s1e3", "s1e4", "s1e5",
+      "s2e1", "s2e2", "s2e3", "s2e4", "s2e5",
+    ]);
+  });
+
+  it("reaches back into the previous season from a season opener", () => {
+    const eps = [...season(1, 5), ...season(2, 5)];
+    const current = eps[5]; // S2E1
+    const strip = adjacentEpisodes(current, eps);
+    expect(strip.slice(0, 3).map((e) => e.id)).toEqual(["s1e3", "s1e4", "s1e5"]);
+    expect(strip[3].id).toBe("s2e1");
+  });
+
+  it("orders by season then episode, never interleaving seasons", () => {
+    const eps = [...season(2, 3), ...season(1, 3)]; // deliberately out of order
+    const current = eps[3]; // S1E1
+    const strip = adjacentEpisodes(current, eps);
+    expect(strip.map((e) => e.id)).toEqual([
+      "s1e1", "s1e2", "s1e3", "s2e1", "s2e2", "s2e3",
+    ]);
+  });
+
+  it("sorts specials (season 0) after the numbered seasons", () => {
+    const eps = [...season(0, 2), ...season(1, 2)];
+    const current = eps[2]; // S1E1
+    const strip = adjacentEpisodes(current, eps);
+    expect(strip.map((e) => e.id)).toEqual(["s1e1", "s1e2", "s0e1", "s0e2"]);
   });
 
   it("splices in a directly-fetched episode absent from the list (ID mismatch)", () => {
@@ -93,5 +123,42 @@ describe("adjacentEpisodes", () => {
     const current = ep("mystery", null, 3); // no season number
     const strip = adjacentEpisodes(current, eps);
     expect(strip.length).toBeGreaterThan(1);
+    // Anchored at its episode number, not dumped at one end of the list.
+    expect(strip.indexOf(current)).toBeGreaterThan(0);
+    expect(strip.indexOf(current)).toBeLessThan(strip.length - 1);
+  });
+});
+
+describe("compareSeriesOrder", () => {
+  it("orders by season, then episode", () => {
+    expect(compareSeriesOrder(ep("a", 1, 9), ep("b", 2, 1))).toBeLessThan(0);
+    expect(compareSeriesOrder(ep("a", 2, 1), ep("b", 2, 2))).toBeLessThan(0);
+    expect(compareSeriesOrder(ep("a", 2, 2), ep("b", 2, 2))).toBe(0);
+  });
+
+  it("puts specials last", () => {
+    expect(compareSeriesOrder(ep("a", 0, 1), ep("b", 1, 1))).toBeGreaterThan(0);
+    expect(compareSeriesOrder(ep("a", 0, 1), ep("b", 9, 1))).toBeGreaterThan(0);
+  });
+
+  it("falls back to episode number when a season is unknown", () => {
+    expect(compareSeriesOrder(ep("a", null, 2), ep("b", 1, 5))).toBeLessThan(0);
+  });
+});
+
+describe("stripCardLabel", () => {
+  const current = ep("cur", 2, 4);
+
+  it("shows a bare episode number within the current season", () => {
+    expect(stripCardLabel(ep("a", 2, 6), current)).toBe("6.");
+  });
+
+  it("shows SxEy once the card crosses a season boundary", () => {
+    expect(stripCardLabel(ep("a", 3, 1), current)).toBe("S3E1");
+    expect(stripCardLabel(ep("a", 1, 8), current)).toBe("S1E8");
+  });
+
+  it("degrades to the episode number when the season is unknown", () => {
+    expect(stripCardLabel(ep("a", null, 7), current)).toBe("7.");
   });
 });