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/core/executions/NukeExecution.test.ts

@@ -40,6 +40,8 @@ describe("NukeExecution", () => {
 
     player = game.player("player_id");
     otherPlayer = game.player("other_id");
+
+    player.conquer(game.ref(1, 1));
   });
 
   test("nuke should destroy buildings and redraw out of range buildings", async () => {
@@ -76,6 +78,7 @@ describe("NukeExecution", () => {
   });
 
   test("nuke should only be targetable near src and dst", async () => {
+    player.buildUnit(UnitType.MissileSilo, game.ref(1, 1), {});
     const nukeExec = new NukeExecution(
       UnitType.AtomBomb,
       player,