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/EpisodeRow.svelte

@@ -10,15 +10,21 @@
   interface Props {
     episode: MediaItem;
     focused?: boolean;
+    /**
+     * This is the episode the viewer is up to. Marked and scrolled to when the
+     * series page opens, so a viewer four seasons deep lands on their place
+     * instead of the top of season 1. TRACES: UR-062 | DR-102
+     */
+    current?: boolean;
     onclick?: () => void;
   }
 
-  let { episode, focused = false, onclick }: Props = $props();
+  let { episode, focused = false, current = false, onclick }: Props = $props();
 
   let buttonRef: HTMLButtonElement | null = null;
 
   onMount(() => {
-    if (focused && buttonRef) {
+    if ((focused || current) && buttonRef) {
       // Scroll into view with some offset from top
       setTimeout(() => {
         buttonRef?.scrollIntoView({ behavior: "smooth", block: "center" });
@@ -51,7 +57,11 @@
 <button
   bind:this={buttonRef}
   type="button"
-  class="group/row flex gap-4 w-full text-left p-3 rounded-lg hover:bg-[var(--color-surface-hover)] transition-colors {focused ? 'ring-2 ring-[var(--color-jellyfin)] bg-[var(--color-surface)]' : ''}"
+  class="group/row flex gap-4 w-full text-left p-3 rounded-lg hover:bg-[var(--color-surface-hover)] transition-colors {focused
+    ? 'ring-2 ring-[var(--color-jellyfin)] bg-[var(--color-surface)]'
+    : current
+      ? 'ring-2 ring-yellow-400 bg-[var(--color-surface)]'
+      : ''}"
   {onclick}
 >
   <!-- Thumbnail -->
@@ -137,6 +147,13 @@
           <h3 class="text-white font-medium truncate group-hover/row:text-[var(--color-jellyfin)] transition-colors">
             {truncateMiddle(episode.name, 56)}
           </h3>
+          {#if current}
+            <span
+              class="flex-shrink-0 px-2 py-0.5 rounded bg-yellow-400 text-black text-xs font-semibold"
+            >
+              Up next
+            </span>
+          {/if}
           <!-- Played indicator -->
           {#if episode.userData?.isPlayed}
             <svg class="w-4 h-4 flex-shrink-0 text-[var(--color-jellyfin)]" fill="currentColor" viewBox="0 0 24 24">