Self-hosted relay: Invite UI is missing and external members cannot join the community via relay URL

## Describe the bug

I am running a self-hosted Buzz community on a Hostinger VPS using the Buzz Docker deployment.

The relay itself is working correctly for my account, and I am the owner/admin of the community.

However, I am unable to invite another user to the same community.

First, there is no **Invite** or **Relay Access** section available in Settings, so I cannot generate an invite link or invite code for another user.

This appears to be related to #4209, but I am also experiencing an additional issue when another user tries to join the relay directly.

The external user:

* Installed the Buzz Desktop app.
* Created a new Buzz profile.
* Selected **Join a community**.
* Entered my self-hosted `wss://...` relay URL.
* Completed the connection flow.

However, after joining, the user only sees their **personal community/workspace**. My existing self-hosted community, channels, and workspace do not appear.

The user also tried **Add community → Join a community** again with the same relay URL, but the result was unchanged.

Interestingly, in the external user's Buzz profile, information associated with my self-hosted relay is visible, including the name associated with the VPS/Buzz relay container.

This suggests that Buzz is at least discovering or connecting to the relay, but the user is not actually being added to or shown the same community that I am using.

## Steps to reproduce

1. Deploy Buzz as a self-hosted Docker deployment on a Hostinger VPS.
2. Configure and connect to the relay as the community owner/admin.
3. Open Buzz Desktop as the owner.
4. Open Settings.
5. Observe that there is no **Invite** or **Relay Access** UI.
6. On another computer, install Buzz Desktop.
7. Create a new Buzz profile.
8. Select **Join a community**.
9. Enter the self-hosted relay URL:
`wss://...`
10. Complete the join flow.
11. Observe that only the user's personal community/workspace is shown.
12. Try **Add community → Join a community** again using the same relay URL.
13. The self-hosted community still does not appear.
14. Check the external user's Buzz profile and observe that information identifying the self-hosted relay is present.

## Expected behavior

As the owner/admin of a self-hosted community, I expect to have a supported way to invite additional members.

Ideally, one of the following should work:

* The owner should have access to an **Invite / Relay Access** UI and be able to generate an invite.
* Or an external user joining through the self-hosted relay URL should be added to the existing community and see that community after a successful connection.

After joining, the external user should see the same self-hosted community and its available channels rather than only their personal community.

## Actual behavior

The owner has no Invite / Relay Access UI.

The external user can enter the self-hosted relay URL without an obvious connection error, and the relay appears in the user's profile information, but the actual self-hosted community never appears.

The user remains in their personal community/workspace.

## Version and platform

* Buzz version: latest available version
* Owner OS: macOS
* External member OS: Windows
* Server: Hostinger VPS
* Deployment: Buzz Docker / self-hosted relay

## Logs / additional context

The self-hosted relay is operational for the owner account.

Current relevant configuration:

```env
BUZZ_REQUIRE_RELAY_MEMBERSHIP=false
RELAY_OWNER_PUBKEY=
```

The relay owner configuration is present and the owner/admin account can use the self-hosted community normally.

This may be related to #4209 (**Invite / Relay Access UI is missing for self-hosted communities**), but this report also covers the case where another Buzz Desktop user enters the relay URL successfully yet still cannot see or join the existing community.

I would like to clarify what the currently supported onboarding flow is for adding additional users to a self-hosted Buzz community.

If an invite is required, how is a self-hosted community owner expected to generate one when the Invite UI is unavailable?

Start with the Settings invite flow and the Desktop “Join a community” flow described in the report. Trace how BUZZ_REQUIRE_RELAY_MEMBERSHIP and RELAY_OWNER_PUBKEY affect relay membership, then verify the owner can invite a user and that the invited user sees the existing community rather than only a personal workspace.

Written by the indexing model from the issue text.