chore: clear clippy warnings and refresh the GUI README

`cargo clippy --fix`: drop needless borrows in interactive.rs, remove an
unneeded `return`, and derive `Default` for `HostState` / the config struct
instead of hand-writing it. No behaviour change.

README: the GUI host screen now lists connected viewers with a Kick button
and notifies on join/leave — update the description, which still mentioned
only a "live viewer count".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/common/config.rs

@@ -37,18 +37,15 @@ pub struct BandwidthEntry {
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "lowercase")]
+#[derive(Default)]
 pub enum BandwidthStatus {
+    #[default]
     Unmeasured,
     Measured,
     Skipped,
     Failed,
 }
 
-impl Default for BandwidthStatus {
-    fn default() -> Self {
-        Self::Unmeasured
-    }
-}
 
 fn default_status() -> BandwidthStatus {
     BandwidthStatus::Unmeasured