chore(rust): clear the clippy backlog and finish the poison-tolerant lock sweep

`cargo clippy --all-targets` went from 51 warnings (23 in the lib) to zero.
Most were mechanical — needless borrows, `assert_eq!` against a bool literal,
`vec!` where an array does, `or_insert_with(Vec::new)`, a loop index used only
to index — and were applied with `clippy --fix`, then reviewed line by line.
That review caught one auto-fix that was *not* semantically neutral: dropping
the redundant `use hostname;` left its `#[cfg(target_os = "linux")]` orphaned
directly above `SERVICE_NAME`, which would have silently cfg'd the constant out
of every non-Linux build. Removed the stray attribute with the import.

Where a lint asked for a risky change rather than a better one, it is suppressed
with a comment saying why:

- `too_many_arguments` on five `#[tauri::command]` handlers and
  `ThumbnailCache::save_thumbnail` — most of the arity is `State<'_, _>`
  injection, and a parameter struct would change the IPC contract and the
  generated TypeScript for no readability gain.
- `large_enum_variant` on `PlayerStatusEvent` and `AutoplayDecision` — both are
  serde + specta wire types emitted a handful of times a second, never bulk
  allocated; boxing would have to stay invisible to the generated bindings while
  every match arm gained a deref.
- `await_holding_lock` on the `hybrid`/`offline` test modules — the guard is a
  test-only serialisation lock for the process-global `INCLUDE_CATALOG_BROWSE`
  flag, and the await it spans *is* the critical section. Each `#[tokio::test]`
  gets its own single-threaded runtime, so this is not the production deadlock
  class the lint targets; restructuring would reintroduce the flag race.

Real fixes elsewhere: `JellyfinItem::to_media_item` takes `self` by value, so it
is now `into_media_item`; the five-tuple episode row in the download commands
has a named `EpisodeRow` alias; the mpv `PropertyChange` arm matches
`name: "pause"` instead of guarding on it.

Also converted the last 27 raw `.lock().unwrap()` call sites to `lock_safe()`,
completing the `MutexSafe`/`RwLockSafe` convention. All of them turned out to be
in test modules — production code was already clean — so this is consistency
rather than a fix. The two raw locks in `utils/lock.rs` stay raw on purpose:
those tests deliberately poison a mutex to prove the helpers recover from it.

Pure refactoring: all 698 tests still pass.

src-tauri/src/commands/download/mod.rs

@@ -19,6 +19,10 @@ mod smart_cache;
 pub use pinning::*;
 pub use smart_cache::*;
 
+/// One row of the series episode listing used when queueing a whole series:
+/// `(id, name, season_name, index_number, parent_index_number)`.
+type EpisodeRow = (String, String, Option<String>, Option<i32>, Option<i32>);
+
 /// Wrapper for DownloadManager to be used as Tauri state
 pub struct DownloadManagerWrapper(pub Mutex<DownloadManager>);
 
@@ -596,6 +600,10 @@ pub(crate) async fn queue_album_tracks(
 /// TRACES: UR-018, UR-055 | DR-173 | UT-170
 #[tauri::command]
 #[specta::specta]
+// Three of the eight arguments are Tauri `State<'_, _>` injections plus the
+// `AppHandle`, not caller input. Folding the rest into a struct would change the
+// IPC contract and the generated TypeScript for no readability gain.
+#[allow(clippy::too_many_arguments)]
 pub async fn download_album(
     db: State<'_, DatabaseWrapper>,
     repository: State<'_, crate::commands::repository::RepositoryManagerWrapper>,
@@ -807,7 +815,7 @@ pub async fn download_series(
         vec![QueryParam::String(series_id)],
     );
 
-    let episodes: Vec<(String, String, Option<String>, Option<i32>, Option<i32>)> = db_service
+    let episodes: Vec<EpisodeRow> = db_service
         .query_many(episodes_query, |row| {
             Ok((
                 row.get(0)?,
@@ -912,6 +920,10 @@ pub async fn download_series(
 /// Queue all episodes of a specific season for download
 #[tauri::command]
 #[specta::specta]
+// One of the eight arguments is a Tauri `State<'_, _>` injection; the rest are
+// the season's identifying fields. Folding them into a struct would change the
+// IPC contract and the generated TypeScript for no readability gain.
+#[allow(clippy::too_many_arguments)]
 pub async fn download_season(
     db: State<'_, DatabaseWrapper>,
     season_id: String,
@@ -2307,7 +2319,7 @@ pub async fn delete_downloads_under(
          )";
 
     let file_query = Query::with_params(
-        &format!("SELECT d.file_path FROM downloads d WHERE {SCOPE}"),
+        format!("SELECT d.file_path FROM downloads d WHERE {SCOPE}"),
         vec![
             QueryParam::String(user_id.clone()),
             QueryParam::String(item_id.clone()),
@@ -2323,7 +2335,7 @@ pub async fn delete_downloads_under(
         .map_err(|e| e.to_string())?;
 
     let delete_query = Query::with_params(
-        &format!("DELETE FROM downloads WHERE id IN (SELECT d.id FROM downloads d WHERE {SCOPE})"),
+        format!("DELETE FROM downloads WHERE id IN (SELECT d.id FROM downloads d WHERE {SCOPE})"),
         vec![
             QueryParam::String(user_id),
             QueryParam::String(item_id.clone()),