refactor(simulation): derive Default for MonologueState (clippy)

After #878 removed the `character` field, the manual Default impl is
derivable. Clippy flags this under `derivable_impls` with -D warnings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/simulation/monologue.rs

@@ -119,7 +119,7 @@ impl PostConversationQueue {
 
 /// Tracks monologue state for cooldown and trigger detection.
 /// Attached to the PlayerCharacter entity.
-#[derive(Component, Debug)]
+#[derive(Component, Debug, Default)]
 pub struct MonologueState {
     /// Tick when the last monologue was fired.
     pub last_fired_tick: u64,
@@ -137,19 +137,6 @@ pub struct MonologueState {
     pub last_observation_tick: u64,
 }
 
-impl Default for MonologueState {
-    fn default() -> Self {
-        Self {
-            last_fired_tick: 0,
-            last_position: None,
-            idle_ticks: 0,
-            entered: false,
-            shown_ids: BTreeSet::new(),
-            last_observation_tick: 0,
-        }
-    }
-}
-
 /// Buffer holding the monologue event to include in the next snapshot.
 /// `take()` drains the buffer (consumed once per snapshot).
 #[derive(Component, Debug, Default)]