feat(doomsday-clock): battle-royale style zone gamemode (#4469)

Resolves Issue #4463

## Description:

An optional game mode that (almost) guarantees a finish instead of
letting late-game
stalemates drag on.
Originally called sudden death, renamed to Doomsday clock

Once enabled, every side (each player in FFA, each whole team in team
modes)
must hold a rising share of the map. A side below the bar is skulled;
after a
short warn its troops bleed to zero, forcing consolidation to a winner.

### How it works
- **Rising zone:** a grace period, then the required share ramps up
linearly to
each level with 30s pauses between (a battle-royale "zone"). Levels
track the
  ofstats FFA territory median (3/5/10/20/30%).
- **Four speed presets** (slow / normal / fast / very fast) change only
the pace:
  normal ends ~30 min, very fast ~15.
- **Troop decay:** a linear ramp as a % of max capacity, ~50s from
caught to zero
  (10s warn + ~50s ≈ 1 min total).
- **UI:** a HUD panel (live share vs target, wave/decay countdowns,
red/orange
cues) and an on-map skull above flagged players (blinks in danger,
steady while
  draining).

### Notes for review
- Off by default; no effect on existing games. However, as discussed we
can add it to the modifier pool for public games to see how popular the
gamemode is vs normal play.
- Sim is deterministic (integer-only, in `src/core`), covered by unit +
  integration tests.
- One-line addition to `GameServer.updateGameConfig` so the setting
survives the
  host → server → client round-trip.
- Status is packed into the existing name-pass data slot (`pd4.w`: 0/1/2
=
none/danger/draining); the skull is composited into the icon atlas at
load.

### Testing
`npm test`, `npm run lint`, `npx prettier --check .`, `npm run
build-prod` all pass.

### UI:
<img width="243" height="100" alt="Image"
src="https://github.com/user-attachments/assets/c4c9eeb0-4feb-437d-9aac-b2786a841b74"
/>

Dropdown between slow, normal, fast, very fast

Before zone:
<img width="302" height="175" alt="Image"
src="https://github.com/user-attachments/assets/7359a1ea-4951-446d-a23c-0711fe06cc5d"
/>

Zone started, player not affected the pannel also blinks orange for 10s:
<img width="297" height="175" alt="Image"
src="https://github.com/user-attachments/assets/fcc565a5-d5d0-47a7-97ea-d0ba9d9ad899"
/>

Player affected, grace period (Danger):
<img width="314" height="170" alt="Image"
src="https://github.com/user-attachments/assets/ff96d21e-96f3-4ef9-8190-48eecc7aac0f"
/>

Skull icon blinking over player (everyone sees it) - older screenshot,
the clipping has been fixed
<img width="462" height="145" alt="Image"
src="https://github.com/user-attachments/assets/53899211-33b1-40e1-83f2-77f2096f0cad"
/>

Player affected, grace period ended (Draining):
<img width="360" height="159" alt="Image"
src="https://github.com/user-attachments/assets/4b226d57-da4d-4866-ab5f-db48e4ed1ea2"
/>

Skull icon no longer blinking, everyone can see you are in a state of
decay, and troops are draining:
<img width="732" height="146" alt="image"
src="https://github.com/user-attachments/assets/cd10fedb-6e87-4dfc-9fbf-55d3945a7901"
/>


Skull is visible like alliances icon also on player tab
<img width="558" height="81" alt="Image"
src="https://github.com/user-attachments/assets/6acdbe91-bdd0-40c7-942b-3990d4dae87f"
/>

(just UI example, best way to see it is to hop on a solo game and play
against AI)

## 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/core/configuration/Config.ts

@@ -1,6 +1,7 @@
 import { z } from "zod";
 import { PlayerView } from "../../client/view";
 import { AssetManifest } from "../AssetUrls";
+import { DoomsdayClockSpeed } from "../game/DoomsdayClock";
 import {
   Difficulty,
   Game,
@@ -80,6 +81,21 @@ export const JwksSchema = z.object({
 /** SAM launcher construction duration in ticks (non-instant-build). */
 export const SAM_CONSTRUCTION_TICKS = 30 * 10;
 
+// Doomsday Clock tunables (anti-stall). Off unless enabled in GameConfig.
+// Times in seconds. The required map share rises in waves (levels + times in
+// DoomsdayClock.ts, chosen by `speed`). A side caught below the bar gets a
+// warnSeconds cooldown ("Danger, decay in Xs"), then troops bleed to zero: the
+// warn (10s) + the linear drain (~55s from full troops, sooner with fewer troops
+// or a shrinking territory) make ~1 minute from caught to wiped out.
+const DOOMSDAY_CLOCK_DEFAULTS = {
+  enabled: false,
+  speed: "normal" as DoomsdayClockSpeed,
+  warnSeconds: 10, // cooldown before decay after the bar catches you
+  drainStartPercent: 2, // starts bleeding at once (already beats troop income)
+  drainMaxPercent: 6,
+  drainRampSeconds: 50, // ramps LINEARLY to the max over this long
+};
+
 export class Config {
   private unitInfoCache = new Map<UnitType, UnitInfo>();
   constructor(
@@ -101,6 +117,21 @@ export class Config {
   traitorDuration(): number {
     return 30 * 10; // 30 seconds
   }
+
+  // Doomsday Clock config, resolved against defaults. One read per tick.
+  doomsdayClockConfig(): typeof DOOMSDAY_CLOCK_DEFAULTS {
+    const c = this._gameConfig.doomsdayClock;
+    const d = DOOMSDAY_CLOCK_DEFAULTS;
+    return {
+      enabled: c?.enabled ?? d.enabled,
+      speed: c?.speed ?? d.speed,
+      // Drain/warn tuning is internal (not wire-configurable): always defaults.
+      warnSeconds: d.warnSeconds,
+      drainStartPercent: d.drainStartPercent,
+      drainMaxPercent: d.drainMaxPercent,
+      drainRampSeconds: d.drainRampSeconds,
+    };
+  }
   spawnImmunityDuration(): Tick {
     return (
       this._gameConfig.spawnImmunityDuration ?? DEFAULT_SPAWN_IMMUNITY_TICKS