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/knowledge/events.rs

@@ -100,7 +100,7 @@ pub fn decay_knowledge(
     mut knowledge_query: Query<&mut KnowledgeGraph>,
 ) {
     // Decay runs every 10 ticks (1 game-minute per D-031)
-    if time.tick % 10 != 0 {
+    if !time.tick.is_multiple_of(10) {
         return;
     }
     for mut kg in knowledge_query.iter_mut() {

server/src/knowledge/types.rs

@@ -70,9 +70,10 @@ impl KnowledgeConfidence {
 
 /// Temporal/logical state of a knowledge entry.
 /// Orthogonal to confidence: a KnowsDetails entry can be Active or Contradicted.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default, Serialize, Deserialize)]
 pub enum KnowledgeState {
     /// Currently believed true. Default state.
+    #[default]
     Active,
     /// Conflicting information exists. Both conflicting entries receive this state.
     /// Triggers monologue event when set. THE FRIEND arc detector.
@@ -82,12 +83,6 @@ pub enum KnowledgeState {
     Stale,
 }
 
-impl Default for KnowledgeState {
-    fn default() -> Self {
-        Self::Active
-    }
-}
-
 // --- Knowledge Source ---
 
 /// How knowledge was acquired. Tracked per-entry for provenance.
@@ -119,9 +114,10 @@ pub enum SoundRange {
 /// Relationship state drives D-033 entity color rendering.
 /// Derived from knowledge + NPC relationship axes (D-024).
 /// Client maps this to color palette defined in D-033.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default, Serialize, Deserialize)]
 pub enum RelationshipState {
     /// No prior knowledge. Teal #4a9ebb.
+    #[default]
     Unknown,
     /// Recognized, neutral-to-positive. Soft green #6bc9a6.
     Known,
@@ -133,12 +129,6 @@ pub enum RelationshipState {
     Hostile,
 }
 
-impl Default for RelationshipState {
-    fn default() -> Self {
-        Self::Unknown
-    }
-}
-
 // --- Entity Knowledge ---
 
 /// What entity A knows about entity B.
@@ -205,9 +195,10 @@ impl Default for DecayThresholds {
 
 /// How an entity appears in the observer snapshot.
 /// Extends VisibleEntity for knowledge-based rendering.
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Default, Serialize, Deserialize)]
 pub enum EntityVisibility {
     /// Currently in line of sight.
+    #[default]
     Visible,
     /// Not in LOS but remembered from knowledge graph.
     Remembered {
@@ -215,9 +206,3 @@ pub enum EntityVisibility {
         age_ticks: u64,
     },
 }
-
-impl Default for EntityVisibility {
-    fn default() -> Self {
-        Self::Visible
-    }
-}