style: apply rustfmt to establish clean baseline before refactor

Pre-refactor baseline state:
- 79 lib tests + 3 integration tests pass (1 integration test #[ignore])
- cargo clippy --all-targets -- -D warnings clean
- cargo build --release clean

No semantic changes; only rustfmt drift correction across 6 files.

src/backend_detect.rs

@@ -113,25 +113,23 @@ fn check_portal_available() -> bool {
 
         // The most likely operation to hang — requires actual Portal-side work.
         // 最可能卡住的操作，需要 Portal 端实际处理。
-        let version = match tokio::time::timeout(
-            PORTAL_DBUS_TIMEOUT,
-            inner.get_property::<u32>("version"),
-        )
-        .await
-        {
-            Ok(Ok(version)) => {
-                tracing::info!("Portal ScreenCast available (version: {version})");
-                true
-            }
-            Ok(Err(e)) => {
-                tracing::info!("Portal ScreenCast version query failed: {e}");
-                false
-            }
-            Err(_) => {
-                log_portal_unresponsive("querying ScreenCast version");
-                false
-            }
-        };
+        let version =
+            match tokio::time::timeout(PORTAL_DBUS_TIMEOUT, inner.get_property::<u32>("version"))
+                .await
+            {
+                Ok(Ok(version)) => {
+                    tracing::info!("Portal ScreenCast available (version: {version})");
+                    true
+                }
+                Ok(Err(e)) => {
+                    tracing::info!("Portal ScreenCast version query failed: {e}");
+                    false
+                }
+                Err(_) => {
+                    log_portal_unresponsive("querying ScreenCast version");
+                    false
+                }
+            };
         version
     })
 }