implement waves

src/lib/sim/Building.h

@@ -52,6 +52,17 @@ struct ConstructionSite
     Tick         completesAt   = 0;             // 0 = queued but not yet started
 };
 
+// Weapon state for stationary structures (defence stations).
+// Distinct from Ship::Weapon; stations have no movement intent.
+struct StationWeapon
+{
+    float damage;
+    float range;
+    float fireRateHz;
+    float cooldownTicks;
+    std::optional<EntityId> currentTarget;
+};
+
 // A fully constructed, operational building.
 struct Building
 {
@@ -73,4 +84,7 @@ struct Building
     std::vector<Port>   outputPorts;
     std::vector<Port>   inputPorts;  // perimeter tiles (minus output-port tiles),
                                      // direction pointing INTO building
+
+    // Set only for defence stations; nullopt for all other building types.
+    std::optional<StationWeapon> weapon;
 };