feat: grant Elysian role on auth and prompt non-members to join (#134)

## Summary

- Grants the Elysian Discord role to players on login/registration and persists an `inGuild` flag on the Player record
- Connects to the Discord Gateway via WebSocket to keep `inGuild` in sync as players join or leave the server
- Shows a dismissible "Join our community" modal to players who are not yet in the guild
- Hardens `inGuild` exposure through the load endpoint and game context
- Moves all non-secret Discord IDs (guild, role, client, redirect URI) out of env vars and into hardcoded constants; removes them from `prod.env`

## Test plan

- [ ] Lint, build, and test pipeline passes (100% coverage maintained)
- [ ] New player auth grants Elysian role and sets `inGuild: true`
- [ ] Existing player auth re-attempts role grant and updates `inGuild`
- [ ] Join community modal appears for players not in the guild
- [ ] Modal does not reappear within the same browser session after dismissal
- [ ] Gateway correctly sets `inGuild: true/false` on member add/remove events

✨ This issue was created with help from Hikari~ 🌸

Reviewed-on: #134
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

apps/api/src/services/gateway.ts

@@ -0,0 +1,182 @@
+/**
+ * @file Discord Gateway WebSocket client for listening to guild member events.
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+/* eslint-disable max-lines-per-function -- WebSocket gateway requires sequential event handler setup */
+import { prisma } from "../db/client.js";
+import { logger } from "./logger.js";
+
+const discordGuildId = "1354624415861833870";
+
+/**
+ * Discord Gateway opcodes used by this client.
+ */
+const gatewayOpcodes = {
+  dispatch:     0,
+  heartbeat:    1,
+  heartbeatAck: 11,
+  hello:        10,
+  identify:     2,
+} as const;
+
+/**
+ * GUILD_MEMBERS privileged intent bitmask.
+ */
+/* eslint-disable-next-line no-bitwise -- Bitwise shift required for Discord intent bitmask */
+const guildMembersIntent = 1 << 1;
+
+/**
+ * Updates the inGuild flag for a player when they join the configured guild.
+ * No-ops silently if the Discord user has no player record.
+ * @param discordId - The Discord user ID of the member who joined.
+ * @param guildId - The ID of the guild they joined.
+ * @returns A promise that resolves when the update attempt completes.
+ */
+const handleGuildMemberAdd = async(
+  discordId: string,
+  guildId: string,
+): Promise<void> => {
+  if (guildId !== discordGuildId) {
+    return;
+  }
+  try {
+    await prisma.player.updateMany({
+      data:  { inGuild: true },
+      where: { discordId },
+    });
+  } catch (error) {
+    void logger.error(
+      "gateway_member_add",
+      error instanceof Error
+        ? error
+        : new Error(String(error)),
+    );
+  }
+};
+
+/**
+ * Updates the inGuild flag for a player when they leave the configured guild.
+ * No-ops silently if the Discord user has no player record.
+ * @param discordId - The Discord user ID of the member who left.
+ * @param guildId - The ID of the guild they left.
+ * @returns A promise that resolves when the update attempt completes.
+ */
+const handleGuildMemberRemove = async(
+  discordId: string,
+  guildId: string,
+): Promise<void> => {
+  if (guildId !== discordGuildId) {
+    return;
+  }
+  try {
+    await prisma.player.updateMany({
+      data:  { inGuild: false },
+      where: { discordId },
+    });
+  } catch (error) {
+    void logger.error(
+      "gateway_member_remove",
+      error instanceof Error
+        ? error
+        : new Error(String(error)),
+    );
+  }
+};
+
+// eslint-disable-next-line capitalized-comments -- v8 ignore directive must be lowercase
+/* v8 ignore next 95 -- @preserve */
+/**
+ * Connects to the Discord Gateway and listens for guild member events.
+ * Reconnects automatically on close or error.
+ * Requires the GUILD_MEMBERS privileged intent to be enabled in the Discord Developer Portal.
+ */
+const connectGateway = (): void => {
+  const botToken = process.env.DISCORD_BOT_TOKEN;
+  if (botToken === undefined || botToken === "") {
+    void logger.log("info", "Gateway: no bot token configured, skipping");
+    return;
+  }
+
+  const ws = new WebSocket("wss://gateway.discord.gg/?v=10&encoding=json");
+  let heartbeatInterval: ReturnType<typeof setInterval> | null = null;
+  let lastSequence: number | null = null;
+
+  const stopHeartbeat = (): void => {
+    if (heartbeatInterval !== null) {
+      clearInterval(heartbeatInterval);
+      heartbeatInterval = null;
+    }
+  };
+
+  ws.addEventListener("message", (event) => {
+    /* eslint-disable-next-line @typescript-eslint/consistent-type-assertions -- Gateway payload is JSON */
+    const payload = JSON.parse(event.data as string) as {
+      op: number;
+      d:  unknown;
+      s:  number | null;
+      t:  string | null;
+    };
+
+    if (payload.s !== null) {
+      lastSequence = payload.s;
+    }
+
+    if (payload.op === gatewayOpcodes.hello) {
+      /* eslint-disable-next-line @typescript-eslint/consistent-type-assertions, @typescript-eslint/naming-convention -- HELLO d shape; Discord API snake_case */
+      const helloData = payload.d as { heartbeat_interval: number };
+      const heartbeatMs = helloData.heartbeat_interval;
+      heartbeatInterval = setInterval(() => {
+        ws.send(JSON.stringify({
+          d:  lastSequence,
+          op: gatewayOpcodes.heartbeat,
+        }));
+      }, heartbeatMs);
+
+      ws.send(JSON.stringify({
+        d: {
+          intents:    guildMembersIntent,
+          properties: { browser: "elysium", device: "elysium", os: "linux" },
+          token:      botToken,
+        },
+        op: gatewayOpcodes.identify,
+      }));
+    }
+
+    if (payload.op === gatewayOpcodes.dispatch && payload.t !== null) {
+      /* eslint-disable-next-line @typescript-eslint/consistent-type-assertions, @typescript-eslint/naming-convention -- dispatch payload shape; Discord API snake_case */
+      const data = payload.d as { user?: { id: string }; guild_id?: string };
+      const discordId = data.user?.id;
+      const guildId = data.guild_id;
+
+      if (discordId === undefined || guildId === undefined) {
+        return;
+      }
+
+      if (payload.t === "GUILD_MEMBER_ADD") {
+        void handleGuildMemberAdd(discordId, guildId);
+      } else if (payload.t === "GUILD_MEMBER_REMOVE") {
+        void handleGuildMemberRemove(discordId, guildId);
+      }
+    }
+  });
+
+  ws.addEventListener("close", () => {
+    stopHeartbeat();
+    void logger.log("info", "Gateway: connection closed, reconnecting in 5s");
+    setTimeout(connectGateway, 5000);
+  });
+
+  ws.addEventListener("error", (event) => {
+    const message
+      = event instanceof ErrorEvent
+        ? event.message
+        : "WebSocket error";
+    void logger.error("gateway_error", new Error(message));
+    stopHeartbeat();
+    ws.close();
+  });
+};
+
+export { connectGateway, handleGuildMemberAdd, handleGuildMemberRemove };