refactor: collapse per-env Configs into ClientEnv + ServerEnv (#3906)

## Description:

This is a refactor to simplify config handling.

Replaces the per-environment DevConfig/PreprodConfig/ProdConfig class
hierarchy with two static classes: ClientEnv (browser main thread, reads
from window.BOOTSTRAP_CONFIG) and ServerEnv (Node server, reads from
process.env). The four config classes are deleted, the abstract
DefaultServerConfig is gone, and DefaultConfig is renamed to Config.

The values that flow server → client (gameEnv, numWorkers,
turnstileSiteKey, jwtAudience, instanceId) used to be baked into the
hardcoded per-env classes. They're now real env vars on the server,
embedded into a single window.BOOTSTRAP_CONFIG object in index.html at
request time (alongside the existing gitCommit/assetManifest/cdnBase
globals, which moved into the same object), and read back by ClientEnv
on the client. The dev defaults previously hidden inside DevServerConfig
are now explicit in start:server-dev (NUM_WORKERS=2,
TURNSTILE_SITE_KEY=1x..., JWT_AUDIENCE=localhost, etc.) and in
vite.config.ts's html plugin inject.data. Production deploys plumb
NUM_WORKERS and TURNSTILE_SITE_KEY through deploy.yml (GitHub vars) into
the remote env file; JWT_AUDIENCE is derived from DOMAIN in deploy.sh.
The dynamic /api/instance endpoint is gone — INSTANCE_ID rides along in
BOOTSTRAP_CONFIG now.

ServerEnv is the only thing server code touches; ClientEnv is
browser-only. The two classes have intentional overlap (env, numWorkers,
jwtIssuer, gameCreationRate, workerIndex, etc.) since they derive
identical logic from different sources — there's a TODO in each to
consolidate via a shared helper later. The game-logic Config no longer
stores a ServerConfig/ClientEnv reference and its serverConfig() getter
is gone; the one caller (MultiTabModal) now reads ClientEnv.env()
directly. Worker init no longer carries server-config values since
nothing in the worker actually reads them.

## 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:

evan

src/client/Matchmaking.ts

@@ -1,7 +1,7 @@
 import { html, LitElement } from "lit";
 import { customElement, state } from "lit/decorators.js";
+import { ClientEnv } from "src/client/ClientEnv";
 import { UserMeResponse } from "../core/ApiSchemas";
-import { getRuntimeClientServerConfig } from "../core/configuration/ConfigLoader";
 import { getUserMe, hasLinkedAccount } from "./Api";
 import { getPlayToken } from "./Auth";
 import { BaseModal } from "./components/BaseModal";
@@ -12,7 +12,6 @@ import { translateText } from "./Utils";
 
 @customElement("matchmaking-modal")
 export class MatchmakingModal extends BaseModal {
-  private static instanceIdPromise: Promise<string> | null = null;
   private gameCheckInterval: ReturnType<typeof setInterval> | null = null;
   private connectTimeout: ReturnType<typeof setTimeout> | null = null;
   @state() private connected = false;
@@ -86,11 +85,8 @@ export class MatchmakingModal extends BaseModal {
   }
 
   private async connect() {
-    const config = await getRuntimeClientServerConfig();
-    const instanceId = await MatchmakingModal.getInstanceId();
-
     this.socket = new WebSocket(
-      `${config.jwtIssuer()}/matchmaking/join?instance_id=${encodeURIComponent(instanceId)}`,
+      `${ClientEnv.jwtIssuer()}/matchmaking/join?instance_id=${encodeURIComponent(ClientEnv.instanceId())}`,
     );
     this.socket.onopen = async () => {
       console.log("Connected to matchmaking server");
@@ -131,32 +127,6 @@ export class MatchmakingModal extends BaseModal {
     };
   }
 
-  private static async getInstanceId(): Promise<string> {
-    MatchmakingModal.instanceIdPromise ??= fetch("/api/instance", {
-      cache: "no-store",
-    })
-      .then(async (response) => {
-        if (!response.ok) {
-          throw new Error(
-            `Failed to load instance id: ${response.status} ${response.statusText}`,
-          );
-        }
-
-        const data = (await response.json()) as { instanceId?: string };
-        if (!data.instanceId) {
-          throw new Error("Missing instance id");
-        }
-
-        return data.instanceId;
-      })
-      .catch((error: unknown) => {
-        MatchmakingModal.instanceIdPromise = null;
-        throw error;
-      });
-
-    return MatchmakingModal.instanceIdPromise;
-  }
-
   protected async onOpen(): Promise<void> {
     const userMe = await getUserMe();
     // Early return if modal was closed during async operation
@@ -209,8 +179,7 @@ export class MatchmakingModal extends BaseModal {
     if (this.gameID === null) {
       return;
     }
-    const config = await getRuntimeClientServerConfig();
-    const url = `/${config.workerPath(this.gameID)}/api/game/${this.gameID}/exists`;
+    const url = `/${ClientEnv.workerPath(this.gameID)}/api/game/${this.gameID}/exists`;
 
     const response = await fetch(url, {
       method: "GET",