Add e2e test for cross-client query invalidation via Centrifugo

[valentin0h]

Summary

• Adds a two-browser Playwright e2e test that verifies the full realtime query invalidation pipeline: mutation → Centrifugo publish → WebSocket broadcast → QueryInvalidationSubscriber → queryClient.invalidateQueries → query refetch → UI update
• Adds Centrifugo env vars to dev:e2e script and playwright.config.ts
• Starts a Centrifugo Docker container in the CI workflow before running e2e tests

How the test works

Two separate browser contexts, two different users, zero page refreshes:

1. User A (org admin) loads the landing page — listJoinRequests query fires, registers on profileJoinRequest:target channel, WebSocket subscription opens
2. User B (individual from another org) visits User A's org profile and clicks "Request" — createJoinRequest mutation publishes to Centrifugo on the same channel
3. Centrifugo broadcasts → User A's QueryInvalidationSubscriber receives → invalidateQueries → listJoinRequests refetches

Primary assertion: Network intercept (page.waitForResponse) catches the listJoinRequests refetch on User A's page — direct proof the invalidation pipeline triggered a refetch without navigation.

Secondary assertion: UI shows "Join requests" panel and "wants to join your organization" text on User A's page.

Files changed

File	Change
tests/e2e/tests/query-invalidation.spec.ts	New test
tests/e2e/playwright.config.ts	Centrifugo env vars
package.json	Centrifugo env vars in dev:e2e, end-to-end script alias
.github/workflows/e2e-tests.yml	Start Centrifugo container before e2e tests