BUG FIX: Gold double deduction + Rmoval of UnitType.Construction (#2378)

## Description:

- Removed the temporary UnitType.Construction and embedded construction
state into real units via isUnderConstruction().
- Centralized non-structure spawning to perform a single validation
right before unit creation/launch.
- Updated UI layers to render construction state without relying on the
removed enum.
- Adjusted and created tests to match the new flow and to cover the
no-refundscenarios.

# Tests updated 
- tests/economy/ConstructionGold.test.ts: covers structure cost
deduction and income, tolerant of passive income; ensures no refunds
during construction.
- tests/nukes/HydrogenAndMirv.test.ts: accounts for single-check launch
flow; MIRV test targets a player-owned tile; ensures launch after
payment.
- tests/client/graphics/UILayer.test.ts: mocks now provide
isUnderConstruction and real type strings;

## 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:

CrackeRR1

---------

Co-authored-by: Evan <evanpelle@gmail.com>

tests/ShellRandom.test.ts

@@ -145,7 +145,13 @@ describe("Shell Random Damage", () => {
   });
 
   test("Defense post shell attacks have random damage", () => {
-    const defensePost = new DefensePostExecution(player1, game.ref(coastX, 5));
+    player1.conquer(game.ref(coastX, 5));
+    const spawn = player1.canBuild(UnitType.DefensePost, game.ref(coastX, 5));
+    if (spawn === false) {
+      throw new Error("Unable to build defense post for test");
+    }
+    const defensePostUnit = player1.buildUnit(UnitType.DefensePost, spawn, {});
+    const defensePost = new DefensePostExecution(defensePostUnit);
 
     const target = player2.buildUnit(
       UnitType.Warship,