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/web/src/components/game/gameLayout.tsx

@@ -27,6 +27,7 @@ import { DebugPanel } from "./debugPanel.js";
 import { EditProfileModal } from "./editProfileModal.js";
 import { EquipmentPanel } from "./equipmentPanel.js";
 import { ExplorationPanel } from "./explorationPanel.js";
+import { JoinCommunityModal } from "./joinCommunityModal.js";
 import { LoginBonusModal } from "./loginBonusModal.js";
 import { MilestoneToast } from "./milestoneToast.js";
 import { OfflineModal } from "./offlineModal.js";
@@ -164,6 +165,7 @@ const GameLayout = (): JSX.Element => {
         transcendenceCount={state.transcendence?.count ?? 0}
       />
       <OfflineModal />
+      <JoinCommunityModal />
       {schemaOutdated && !dismissedOutdatedWarning
         ? <OutdatedSchemaModal onDismiss={handleDismissOutdated} />
         : null}

apps/web/src/components/game/joinCommunityModal.tsx

@@ -0,0 +1,70 @@
+/**
+ * @file Modal prompting players to join the NHCarrigan Discord community.
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+import { useCallback, useState, type JSX } from "react";
+import { useGame } from "../../context/gameContext.js";
+
+const sessionKey = "elysium_join_community_dismissed";
+
+/**
+ * Renders a modal prompting the player to join the NHCarrigan Discord server.
+ * Shown once per session when the player is not already in the guild.
+ * @returns The JSX element or null if the player is in the guild or dismissed.
+ */
+const JoinCommunityModal = (): JSX.Element | null => {
+  const { inGuild } = useGame();
+  const [ dismissed, setDismissed ] = useState(
+    () => {
+      return sessionStorage.getItem(sessionKey) === "true";
+    },
+  );
+
+  const handleDismiss = useCallback((): void => {
+    sessionStorage.setItem(sessionKey, "true");
+    setDismissed(true);
+  }, []);
+
+  if (inGuild || dismissed) {
+    return null;
+  }
+
+  return (
+    <div className="modal-overlay">
+      <div className="modal">
+        <h2>{"Join Our Community!"}</h2>
+        <p>
+          {"Did you know Elysium has an active Discord community? "}
+          {"Join to chat with other players, get updates, and earn "}
+          {"the exclusive Elysian role!"}
+        </p>
+        <p className="modal-note">
+          {"You already earn the Elysian role just by playing — "}
+          {"joining lets us show it off in the server!"}
+        </p>
+        <div className="modal-actions">
+          <a
+            className="modal-close-button"
+            href="https://discord.gg/KKe7BaEnQB"
+            onClick={handleDismiss}
+            rel="noreferrer"
+            target="_blank"
+          >
+            {"Join Discord"}
+          </a>
+          <button
+            className="modal-close-button"
+            onClick={handleDismiss}
+            type="button"
+          >
+            {"Maybe later"}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+};
+
+export { JoinCommunityModal };