chore(backend): satisfy cargo fmt

`checks.yml` runs `cargo fmt --check`, and it has been failing since the round-1
audit fixes: I gated those on `cargo build` and `cargo clippy` but never ran fmt,
so three files drifted then and eight more this round. Pure formatting — no
behaviour change; clippy stays at zero and all 70 backend tests still pass.

Worth noting for next time: clippy passing is not evidence fmt does.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/src/models/upload.rs

@@ -150,11 +150,7 @@ impl Upload {
 
     /// Stamp which revision of the derivative pipeline produced this row's preview/display,
     /// so the startup backfill can find rows generated by an older one exactly once.
-    pub async fn set_derivatives_rev(
-        pool: &PgPool,
-        id: Uuid,
-        rev: i16,
-    ) -> Result<(), sqlx::Error> {
+    pub async fn set_derivatives_rev(pool: &PgPool, id: Uuid, rev: i16) -> Result<(), sqlx::Error> {
         sqlx::query("UPDATE upload SET derivatives_rev = $2 WHERE id = $1")
             .bind(id)
             .bind(rev)