Disable build hotkeys after death (#3833)

## Description:

Prevent number-key build shortcuts from opening the unit build ghost
after the player has died.
Keep build hotkeys available only while the player is alive and not in
spawn phase.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:
aotumuri

src/client/InputHandler.ts

@@ -519,10 +519,12 @@ export class InputHandler {
       }
 
       // Two-phase build keybind matching: exact code match first, then digit/Numpad alias.
-      const matchedBuild = this.resolveBuildKeybind(e.code, e.shiftKey);
-      if (matchedBuild !== null) {
-        e.preventDefault();
-        this.setGhostStructure(matchedBuild);
+      if (this.canUseBuildKeybinds()) {
+        const matchedBuild = this.resolveBuildKeybind(e.code, e.shiftKey);
+        if (matchedBuild !== null) {
+          e.preventDefault();
+          this.setGhostStructure(matchedBuild);
+        }
       }
 
       if (this.keybindMatchesEvent(e, this.keybinds.requestAlliance)) {
@@ -943,6 +945,11 @@ export class InputHandler {
     return null;
   }
 
+  private canUseBuildKeybinds(): boolean {
+    const myPlayer = this.gameView.myPlayer?.();
+    return !this.gameView.inSpawnPhase() && myPlayer?.isAlive() === true;
+  }
+
   private getPinchDistance(): number {
     const pointerEvents = Array.from(this.pointers.values());
     const dx = pointerEvents[0].clientX - pointerEvents[1].clientX;