feat(engine): retire D-078 overheard conversation system (#848)

Per R-012: delete conversation.rs, both overheard content files, and
remove all 6 wire-up points (social_plugin, bridge/types, monologue,
voice/integration). Protocol version 22 → 23. Scope confirmed by
#842 audit — npc/ and content/global/ untouched. Surviving NPC
components (NpcName, NpcColorIndex, NpcConversation) migrated to
simulation/npc_components.rs for use by D-080 knowledge propagation.
Also applies pre-existing cargo fmt debt (names.rs and 4 others).

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

server/src/bookmark/mod.rs

@@ -14,7 +14,7 @@ use bevy_app::prelude::*;
 use bevy_ecs::prelude::*;
 
 use crate::bridge::types::{BookmarkCatalog, BookmarkWire, CareerKindWire, SnapshotBuffer};
-use crate::knowledge::{CultureResolver, resolve_culture};
+use crate::knowledge::{resolve_culture, CultureResolver};
 
 /// Immutable registry of bookmark definitions.
 ///
@@ -190,7 +190,10 @@ mod tests {
         assert_eq!(wire.id, "tycoon");
         assert_eq!(wire.career, CareerKindWire::Tycoon);
         assert!(!wire.default_location.is_empty());
-        assert_eq!(wire.allowed_locations.len(), wire.allowed_locations_cultures.len());
+        assert_eq!(
+            wire.allowed_locations.len(),
+            wire.allowed_locations_cultures.len()
+        );
     }
 
     #[test]
@@ -216,6 +219,8 @@ mod tests {
         let r = make_registry();
         let defn = r.get("tycoon").unwrap();
         assert!(defn.allowed_locations.contains(&"GJ 35".to_string()));
-        assert!(!defn.allowed_locations.contains(&"Unknown System".to_string()));
+        assert!(!defn
+            .allowed_locations
+            .contains(&"Unknown System".to_string()));
     }
 }