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/perception/shadowcast.rs

@@ -286,11 +286,9 @@ fn has_line_of_sight(
 
     loop {
         // Check if we hit a blocking tile BEFORE reaching target
-        if (x != x0 || y != y0) && (x != x1 || y != y1) {
-            if is_opaque(x, y) {
-                // Hit an obstacle before reaching target - blocked
-                return false;
-            }
+        if (x != x0 || y != y0) && (x != x1 || y != y1) && is_opaque(x, y) {
+            // Hit an obstacle before reaching target - blocked
+            return false;
         }
 
         // If we reach the target, we can see it