feat: cancel ranked 2v2 matches that don't fill or fully spawn (#4655)

## Problem

A ranked 2v2 that starts with a missing player, or where a matched
player idles through the spawn phase, plays out as a lopsided 2v1 — and
records a ranked result (ELO) for a match that was never fair.

## Solution

Void the match from inside the sim: `WinCheckExecution` runs a one-time
check on the first check tick after the spawn phase ends. For
`rankedType === "2v2"`, if fewer than `maxPlayers` humans have spawned,
the game ends immediately with **no winner**. A player who never joined
isn't in the game start info at all, so the single spawn-count check
covers both the missing-at-start and never-spawned cases.

- `setWinner` now accepts `null` and emits a `WinUpdate` with `winner:
undefined` — the wire schema (`WinnerSchema`) already allowed an absent
winner.
- `WinModal`'s previously-empty `winner === undefined` branch shows
"Match cancelled — not all players spawned" and still votes the
winnerless result to the server, so the winner-vote consensus is reached
and the record archives promptly.
- The archived record simply has no `winner`; the API voids winnerless
ranked records (same shape any ranked game already produces when the
winner vote never reaches consensus).
- Only server change: winner votes are keyed with `JSON.stringify(winner
?? null)`, since `JSON.stringify(undefined)` is not a string and would
break the `VoteRound` key contract.

The check counts via `allPlayers()` rather than `players()`, since the
latter filters out tile-less players — which is exactly what a
never-spawned player is.

Ranked 1v1 is deliberately untouched (the existing last-human-connected
walkover still applies).

## Tests

`tests/Ranked2v2Cancel.test.ts`:
- 3 of 4 players spawn → game ends with a winnerless `WinUpdate`
- a 4th player never joined (absent from start info) → same
- all 4 spawn → no cancellation
- unranked team game short a player → no cancellation

Full suite (2094 tests), tsc, ESLint, and Prettier all pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/client/hud/layers/WinModal.ts

@@ -277,7 +277,14 @@ export class WinModal extends LitElement implements Controller {
     const winUpdates = updates !== null ? updates[GameUpdateType.Win] : [];
     winUpdates.forEach((wu) => {
       if (wu.winner === undefined) {
-        // ...
+        // Match cancelled (e.g. a ranked 2v2 that didn't fill or fully
+        // spawn): the game ends with no winner. Still vote the result to the
+        // server so the record is archived winnerless (never ranked).
+        this.eventBus.emit(new SendWinnerEvent(undefined, wu.allPlayersStats));
+        this._title = translateText("win_modal.match_cancelled");
+        this.isWin = false;
+        history.replaceState(null, "", `${window.location.pathname}?replay`);
+        this.show();
       } else if (wu.winner[0] === "team") {
         this.eventBus.emit(new SendWinnerEvent(wu.winner, wu.allPlayersStats));
         if (wu.winner[1] === this.game.myPlayer()?.team()) {