refactor(server): fix clippy warnings from Rust 1.93

- Use #[derive(Default)] + #[default] instead of manual Default impls
  for FacingDirection, KnowledgeState, RelationshipState, EntityVisibility
- Replace manual modulo check with .is_multiple_of()
- Collapse nested if in shadowcast symmetry check

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

server/src/bridge/types.rs

@@ -47,8 +47,9 @@ pub struct GameTime {
 
 /// 8-directional facing direction, matching movement system.
 /// Used for vision cone computation (D-015) and snapshot wire format.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default, Serialize, Deserialize)]
 pub enum FacingDirection {
+    #[default]
     North,
     Northeast,
     East,
@@ -59,12 +60,6 @@ pub enum FacingDirection {
     Northwest,
 }
 
-impl Default for FacingDirection {
-    fn default() -> Self {
-        FacingDirection::North
-    }
-}
-
 /// A tile visible to the observer with its visibility quality
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct VisibleTile {