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/ClearHistoryButton.svelte

@@ -0,0 +1,94 @@
+<!--
+  Erase watch history for a series or a season.
+
+  The backend does the work (`repository_clear_watch_history` → Jellyfin's
+  mark-unplayed, which is recursive over a container and also zeroes resume
+  positions); this only confirms the intent and reports the outcome. Clearing a
+  series returns it to "never watched", so it reopens on S1E1.
+
+  TRACES: UR-064 | DR-106
+-->
+<script lang="ts">
+  import { auth } from "$lib/stores/auth";
+  import { isServerReachable } from "$lib/stores/connectivity";
+
+  interface Props {
+    /** Series or season id to clear. */
+    itemId: string;
+    /** Name shown in the confirm prompt. */
+    itemName: string;
+    /** What is being cleared, for the prompt wording. */
+    scope: "series" | "season";
+    size?: "sm" | "lg";
+    /** Called after a successful clear so the caller can reload. */
+    onCleared?: () => void;
+  }
+
+  let { itemId, itemName, scope, size = "lg", onCleared }: Props = $props();
+
+  let busy = $state(false);
+
+  const label = $derived(scope === "series" ? "Clear history" : "Clear season history");
+
+  async function handleClick() {
+    if (busy) return;
+
+    const subject = scope === "series" ? `all of “${itemName}”` : `“${itemName}”`;
+    // Destructive and not undoable — always ask, even though the server keeps
+    // no undo of its own.
+    if (
+      !confirm(
+        `Erase watch history for ${subject}?\n\n` +
+          "Every episode is marked unwatched and resume positions are cleared. " +
+          "This cannot be undone."
+      )
+    ) {
+      return;
+    }
+
+    busy = true;
+    try {
+      await auth.getRepository().clearWatchHistory(itemId);
+      onCleared?.();
+    } catch (e) {
+      console.error("Failed to clear watch history:", e);
+      alert(
+        `Could not clear watch history: ${e instanceof Error ? e.message : String(e)}`
+      );
+    } finally {
+      busy = false;
+    }
+  }
+</script>
+
+<button
+  onclick={handleClick}
+  disabled={busy || !$isServerReachable}
+  title={$isServerReachable
+    ? "Mark everything unwatched and clear resume positions"
+    : "Needs a connection to the server"}
+  class="rounded-lg font-medium flex items-center gap-2 transition-colors
+         bg-[var(--color-surface)] hover:bg-[var(--color-surface-hover)]
+         disabled:opacity-40 disabled:cursor-not-allowed
+         {size === 'lg' ? 'px-6 py-2' : 'px-3 py-1.5 text-sm'}"
+>
+  {#if busy}
+    <div
+      class="border-2 border-current border-t-transparent rounded-full animate-spin
+             {size === 'lg' ? 'w-5 h-5' : 'w-4 h-4'}"
+    ></div>
+  {:else}
+    <svg
+      class={size === "lg" ? "w-5 h-5" : "w-4 h-4"}
+      fill="currentColor"
+      viewBox="0 0 24 24"
+    >
+      <path
+        d="M13 3a9 9 0 0 0-9 9H1l3.89 3.89.07.14L9 12H6a7 7 0 1 1 7 7c-1.93
+           0-3.68-.79-4.94-2.06l-1.42 1.42A8.95 8.95 0 0 0 13 21a9 9 0 0 0
+           0-18zm-1 5v5l4.28 2.54.72-1.21-3.5-2.08V8H12z"
+      />
+    </svg>
+  {/if}
+  {busy ? "Clearing…" : label}
+</button>