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-tauri/src/repository/online.rs

@@ -1691,6 +1691,48 @@ impl MediaRepository for OnlineRepository {
         result
     }
 
+    /// `DELETE /Users/{userId}/PlayedItems/{itemId}` — Jellyfin's "mark
+    /// unplayed", which also zeroes the resume position. On a folder (series,
+    /// season) the server applies it recursively to the children.
+    ///
+    /// TRACES: UR-064 | DR-106, JA-033
+    async fn clear_watch_history(&self, item_id: &str) -> Result<(), RepoError> {
+        let endpoint = format!("/Users/{}/PlayedItems/{}", self.user_id, item_id);
+        let url = format!("{}{}", self.server_url, endpoint);
+
+        let result = async {
+            let request = self
+                .http_client
+                .client
+                .delete(&url)
+                .header("X-Emby-Authorization", self.auth_header())
+                .build()
+                .map_err(|e| RepoError::Network {
+                    message: format!("Failed to build request: {}", e),
+                })?;
+
+            let response = self
+                .http_client
+                .request_with_retry(request)
+                .await
+                .map_err(|e| RepoError::Network {
+                    message: e.to_string(),
+                })?;
+
+            if !response.status().is_success() {
+                return Err(RepoError::Server {
+                    message: format!("HTTP {}", response.status()),
+                });
+            }
+
+            Ok(())
+        }
+        .await;
+
+        self.report_outcome(&result).await;
+        result
+    }
+
     async fn get_person(&self, person_id: &str) -> Result<MediaItem, RepoError> {
         let endpoint = format!("/Users/{}/Items/{}", self.user_id, person_id);
         let item: JellyfinItem = self.get_json(&endpoint).await?;