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}