Add retreating warship indicator and warship 2-color treatment

Warships now render with a dedicated center accent band so their state
reads at a glance:
- Normal: center + outer ring share the territory color (2-color look),
  hull uses the border color.
- Angry (attacking): outer ring and center turn red.
- Retreating to repair: the center blinks black.

The warship sprite center moved to its own gray value (100) in the unit
atlas so the shader can drive it via a new fourth replacement band, with
no per-unit-type branching — the missiles' shared 130 blend band is
untouched.

Warship repair-retreat (warshipState.state === "retreating") now feeds
the existing UnitState.retreating boolean in UnitView, which UnitPass
maps to a FLAG_RETREATING instance flag.

src/client/view/UnitView.ts

@@ -53,7 +53,9 @@ function unitStateFromUpdate(u: UnitUpdate): UnitState {
     lastPos: u.lastPos,
     isActive: u.isActive,
     reachedTarget: u.reachedTarget,
-    retreating: u.transportShipState?.isRetreating ?? false,
+    retreating:
+      (u.transportShipState?.isRetreating ?? false) ||
+      u.warshipState?.state === "retreating",
     targetable: u.targetable,
     markedForDeletion: u.markedForDeletion,
     health: u.health ?? null,
@@ -79,7 +81,9 @@ function applyUpdateInPlace(target: UnitState, u: UnitUpdate): void {
   target.lastPos = u.lastPos;
   target.isActive = u.isActive;
   target.reachedTarget = u.reachedTarget;
-  target.retreating = u.transportShipState?.isRetreating ?? false;
+  target.retreating =
+    (u.transportShipState?.isRetreating ?? false) ||
+    u.warshipState?.state === "retreating";
   target.targetable = u.targetable;
   target.markedForDeletion = u.markedForDeletion;
   target.health = u.health ?? null;