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/EpisodeFocusView.svelte

@@ -4,7 +4,11 @@
   import { truncateMiddle } from "$lib/utils/truncateMiddle";
   import type { MediaItem } from "$lib/api/types";
   import CachedImage from "$lib/components/common/CachedImage.svelte";
-  import { isCurrentEpisode as isSameEpisode, adjacentEpisodes as computeAdjacent } from "./episodeStrip";
+  import {
+    isCurrentEpisode as isSameEpisode,
+    adjacentEpisodes as computeAdjacent,
+    stripCardLabel,
+  } from "./episodeStrip";
 
   interface Props {
     episode: MediaItem;
@@ -245,8 +249,8 @@
           <!-- Episode info -->
           <div class="mt-2 space-y-1">
             <div class="flex items-center gap-2">
-              <span class="text-[var(--color-jellyfin)] text-sm font-semibold">
-                {ep.indexNumber || 0}.
+              <span class="text-[var(--color-jellyfin)] text-sm font-semibold whitespace-nowrap">
+                {stripCardLabel(ep, episode)}
               </span>
               <p class="text-white font-medium truncate {isCurrent ? 'text-yellow-400' : 'group-hover/card:text-[var(--color-jellyfin)]'} transition-colors">
                 {ep.name}