Starting gold input in millions with decimal support ✨ (#3349)

## Description:

**Starting gold input: use millions**

Changes the starting gold input in singleplayer and host lobby modals to
accept values in millions (e.g. enter `5` for 5M gold). Supports
decimals like `6.6` for 6.6M. The value is multiplied by 1,000,000
before being sent to the game config.

- Label updated to "Starting Gold (Millions)"
- Input uses float parsing with min 0.1, matching gold multiplier
behavior
- JoinLobbyModal shows clean values without unnecessary decimals (e.g.
"5M" not "5.00M")

Previous

<img width="215" height="139" alt="image"
src="https://github.com/user-attachments/assets/00ce5b6d-f74d-4aee-92f5-c9be1a0a6d3d"
/>
<img width="292" height="74" alt="image"
src="https://github.com/user-attachments/assets/4de936a3-22bd-4ffc-8dbe-0d5066f28186"
/>

Now

<img width="216" height="151" alt="image"
src="https://github.com/user-attachments/assets/489de13e-65b5-4b02-a654-5f6f74b165d1"
/>
<img width="292" height="72" alt="image"
src="https://github.com/user-attachments/assets/51723d5a-55ab-4b7b-bbce-011a586eeb44"
/>

## 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:

FloPinguin

src/client/SinglePlayerModal.ts

@@ -210,18 +210,18 @@ export class SinglePlayerModal extends BaseModal {
         .labelKey=${"single_modal.starting_gold"}
         .checked=${this.startingGold}
         .inputId=${"starting-gold-value"}
-        .inputMin=${0}
-        .inputMax=${1000000000}
-        .inputStep=${100000}
+        .inputMin=${0.1}
+        .inputMax=${1000}
+        .inputStep=${"any"}
         .inputValue=${this.startingGoldValue}
         .inputAriaLabel=${translateText("single_modal.starting_gold")}
         .inputPlaceholder=${translateText(
           "single_modal.starting_gold_placeholder",
         )}
-        .defaultInputValue=${5000000}
-        .minValidOnEnable=${0}
+        .defaultInputValue=${5}
+        .minValidOnEnable=${0.1}
         .onToggle=${this.handleStartingGoldToggle}
-        .onInput=${this.handleStartingGoldValueChanges}
+        .onChange=${this.handleStartingGoldValueChanges}
         .onKeyDown=${this.handleStartingGoldValueKeyDown}
       ></toggle-input-card>`,
     ];
@@ -591,12 +591,17 @@ export class SinglePlayerModal extends BaseModal {
 
   private handleStartingGoldValueChanges = (e: Event) => {
     const input = e.target as HTMLInputElement;
-    const value = parseBoundedIntegerFromInput(input, {
-      min: 0,
-      max: 1000000000,
+    const value = parseBoundedFloatFromInput(input, {
+      min: 0.1,
+      max: 1000,
     });
 
-    this.startingGoldValue = value;
+    if (value === undefined) {
+      this.startingGoldValue = undefined;
+      input.value = "";
+    } else {
+      this.startingGoldValue = value;
+    }
   };
 
   private handleGameModeSelection(value: GameMode) {
@@ -685,7 +690,11 @@ export class SinglePlayerModal extends BaseModal {
                 ? { goldMultiplier: this.goldMultiplierValue }
                 : {}),
               ...(this.startingGold && this.startingGoldValue !== undefined
-                ? { startingGold: this.startingGoldValue }
+                ? {
+                    startingGold: Math.round(
+                      this.startingGoldValue * 1_000_000,
+                    ),
+                  }
                 : {}),
             },
             lobbyCreatedAt: Date.now(), // ms; server should be authoritative in MP