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/simulation/input.rs

@@ -3,11 +3,11 @@
 // PlayerInput: semantic actions (MoveNorth, Interact, UsePerceptionMode, ToggleStance)
 
 use crate::bookmark::{BookmarkRegistry, SelectedBookmark};
-use crate::knowledge::CultureResolverResource;
 use crate::bridge::debug::DebugCommandBuffer;
 use crate::bridge::types::{
     FacingDirection, ObjectType, PlayerAction, PlayerInput, SimError, SimErrorKind, SnapshotBuffer,
 };
+use crate::knowledge::CultureResolverResource;
 use crate::knowledge::{EntityRegistry, StableId};
 use crate::perception::vision_cone::{facing_from_delta, Facing};
 use crate::settings::{SettingsCommand, SettingsCommandBuffer};
@@ -449,7 +449,9 @@ pub fn process_player_input(
                     buf.pending_bookmark_catalog = Some(registry.build_catalog(resolver));
                     tracing::debug!("RequestBookmarkCatalog: catalog staged");
                 } else {
-                    tracing::warn!("RequestBookmarkCatalog: BookmarkRegistry or SnapshotBuffer not available");
+                    tracing::warn!(
+                        "RequestBookmarkCatalog: BookmarkRegistry or SnapshotBuffer not available"
+                    );
                 }
             }
             PlayerAction::ConfirmBookmark {
@@ -1208,7 +1210,11 @@ fn handle_confirm_bookmark(
     if let Some(ref mut sel) = selected_bookmark {
         sel.bookmark_id = Some(bookmark_id.clone());
         sel.starting_location_id = Some(starting_location_id.clone());
-        tracing::info!(bookmark_id, starting_location_id, "ConfirmBookmark: selection recorded");
+        tracing::info!(
+            bookmark_id,
+            starting_location_id,
+            "ConfirmBookmark: selection recorded"
+        );
     }
 }