enable clippy::must_use_candidate, add #[must_use] to the 3 flagged fns

hive-host-sock/src/lib.rs

@@ -487,6 +487,7 @@ pub struct LifecycleScope {
 impl LifecycleScope {
     /// True when nothing is explicitly selected — interpreted as "all
     /// classes" (the bare `hivectl stop` / `start` with no scope flags).
+    #[must_use]
     pub fn is_everything(&self) -> bool {
         !(self.agents || self.ci || self.forge || self.gateway || self.matrix)
             && self.agent_names.is_empty()