refactor(agent): fire_and_forget helper, drop dead default_model + compact_percent fallback, fix stale comment

hive-ag3nt/src/events.rs

@@ -466,12 +466,6 @@ pub fn configured_model() -> Option<&'static str> {
         .map(|s| &*Box::leak(s.into_boxed_str()))
 }
 
-/// Return the model to use when no config and no persisted override exist.
-#[must_use]
-pub fn default_model() -> &'static str {
-    configured_model().unwrap_or(DEFAULT_MODEL)
-}
-
 /// Compiled-in fallback effort level — matches the `effortLevel` baked
 /// into `prompts/claude-settings.json`.
 pub const DEFAULT_EFFORT: &str = "medium";