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/Schemas.ts

@@ -249,6 +249,16 @@ const TeamCountConfigSchema = z.union([
 ]);
 export type TeamCountConfig = z.infer<typeof TeamCountConfigSchema>;
 
+// Doomsday Clock (anti-stall). Below a rising share of the map a player (or, in
+// team modes, their whole team) gets skulled and their troops drain to zero. The
+// required share rises in discrete waves per the `speed` preset (see
+// DoomsdayClock.ts). Only `enabled` and `speed` are wire-configurable; the
+// drain/warn tuning lives in DOOMSDAY_CLOCK_DEFAULTS (Config.ts).
+export const DoomsdayClockConfigSchema = z.object({
+  enabled: z.boolean().optional(),
+  speed: z.enum(["slow", "normal", "fast", "veryfast"]).optional(),
+});
+
 export const GameConfigSchema = z.object({
   gameMap: z.enum(GameMapType),
   difficulty: z.enum(Difficulty),
@@ -258,6 +268,7 @@ export const GameConfigSchema = z.object({
   gameMode: z.enum(GameMode),
   rankedType: z.enum(RankedType).optional(), // Only set for ranked games.
   gameMapSize: z.enum(GameMapSize),
+  doomsdayClock: DoomsdayClockConfigSchema.optional(),
   publicGameModifiers: z
     .object({
       isCompact: z.boolean().optional(),