feat(alliances): custom alliance duration lobby control (#4522)

## Description:

Replaces the "Disable alliances" toggle in the host and single-player
lobbies with a "Custom alliances" control: a toggle plus a minutes input
(0 to 15, step 1).

- 0 minutes disables alliances, same behavior as the old toggle.
- 1 to 15 sets the alliance duration in minutes.

How it works:

- Adds one game-config field, `customAllianceDuration` (minutes).
- `Config.allianceDuration()` uses it when set (and falls back to the
existing 5 minute default), and `Config.disableAlliances()` returns true
when it is 0.
- The legacy `disableAlliances` boolean is still read, so older/archived
configs keep working.
- Validation reuses the existing `parseBoundedIntegerFromInput` and
`toggle-input-card` helpers, so it behaves like the other numeric lobby
options (spawn immunity, max timer).
- The join-lobby screen shows "Alliances: {x}m", or "Alliances:
Disabled" at 0.

<img width="279" height="145" alt="image"
src="https://github.com/user-attachments/assets/5a608e18-3811-4eef-a3a6-9344aaf667fe"
/>
<img width="270" height="152" alt="image"
src="https://github.com/user-attachments/assets/9d8a4d30-51e7-4e82-8ce0-121b12af1c61"
/>
<img width="270" height="144" alt="image"
src="https://github.com/user-attachments/assets/a65b20fb-0db5-4657-a964-880fad7c864e"
/>


## 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

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

zixer._

src/client/JoinLobbyModal.ts

@@ -615,7 +615,7 @@ export class JoinLobbyModal extends BaseModal {
           .value=${`x${c.goldMultiplier}`}
         ></lobby-config-item>`,
       );
-    if (c.disableAlliances)
+    if (c.customAllianceDuration === 0 || c.disableAlliances)
       cards.push(
         html`<lobby-config-item
           .label=${translateText(
@@ -624,6 +624,15 @@ export class JoinLobbyModal extends BaseModal {
           .value=${translateText("common.disabled")}
         ></lobby-config-item>`,
       );
+    else if (typeof c.customAllianceDuration === "number")
+      cards.push(
+        html`<lobby-config-item
+          .label=${translateText(
+            "public_game_modifier.disable_alliances_label",
+          )}
+          .value=${`${c.customAllianceDuration}m`}
+        ></lobby-config-item>`,
+      );
     if (c.waterNukes)
       cards.push(
         html`<lobby-config-item