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/catalog.rs

@@ -496,7 +496,7 @@ pub(crate) async fn requeue_mistyped_video_downloads(
         .collect::<Vec<_>>()
         .join(", ");
 
-    let query = Query::new(&format!(
+    let query = Query::new(format!(
         "UPDATE downloads
          SET status = 'pending', stream_url = NULL, progress = 0,
              bytes_downloaded = 0, started_at = NULL, completed_at = NULL
@@ -563,7 +563,7 @@ where
         ),
         None => String::new(),
     };
-    let rows_query = Query::new(&format!(
+    let rows_query = Query::new(format!(
         "SELECT d.id, d.item_id,
                 COALESCE(
                     d.media_type,
@@ -753,6 +753,7 @@ pub async fn resume_queued_downloads(
 mod tests {
     use super::*;
     use crate::storage::db_service::RusqliteService;
+    use crate::utils::lock::MutexSafe;
     use rusqlite::Connection;
     use std::sync::Mutex;
 
@@ -1012,14 +1013,14 @@ mod tests {
         resolve_pending_download_urls(&db, "/data", None, move |item_id, media_type, _q| {
             let seen = Arc::clone(&seen_c);
             async move {
-                seen.lock().unwrap().push((item_id.clone(), media_type));
+                seen.lock_safe().push((item_id.clone(), media_type));
                 Some(format!("http://resolved/{item_id}"))
             }
         })
         .await
         .unwrap();
 
-        let seen = seen.lock().unwrap().clone();
+        let seen = seen.lock_safe().clone();
         let of = |id: &str| {
             seen.iter()
                 .find(|(i, _)| i == id)
@@ -1045,14 +1046,14 @@ mod tests {
         resolve_pending_download_urls(&db, "/data", None, move |_id, media_type, _q| {
             let seen = Arc::clone(&seen_c);
             async move {
-                *seen.lock().unwrap() = media_type;
+                *seen.lock_safe() = media_type;
                 Some("http://x".to_string())
             }
         })
         .await
         .unwrap();
 
-        assert_eq!(*seen.lock().unwrap(), "audio");
+        assert_eq!(*seen.lock_safe(), "audio");
     }
 
     /// An explicit `media_type` on the row always wins over the item's type.
@@ -1069,14 +1070,14 @@ mod tests {
         resolve_pending_download_urls(&db, "/data", None, move |_id, media_type, _q| {
             let seen = Arc::clone(&seen_c);
             async move {
-                *seen.lock().unwrap() = media_type;
+                *seen.lock_safe() = media_type;
                 Some("http://x".to_string())
             }
         })
         .await
         .unwrap();
 
-        assert_eq!(*seen.lock().unwrap(), "video");
+        assert_eq!(*seen.lock_safe(), "video");
     }
 
     /// Rows already downloaded under the audio default hold an audio-only