style(server): cargo fmt for SPEC-004 Task 2 + Task 4

Pure rustfmt reflow of the Task 2 (machine_uid dedup) and Task 4 (session
reaping) code; no logic change. The CI Build-Server-Linux job gates on
cargo fmt --check, which the two feature commits failed because local
validation ran check/clippy/test but not fmt --check. fmt --check, check,
and clippy -D warnings all clean now.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/main.rs

@@ -283,11 +283,7 @@ async fn main() -> Result<()> {
                         machine.machine_uid.as_deref()
                     };
                     sessions
-                        .restore_offline_machine(
-                            &machine.agent_id,
-                            &machine.hostname,
-                            restore_uid,
-                        )
+                        .restore_offline_machine(&machine.agent_id, &machine.hostname, restore_uid)
                         .await;
                 }
             }