Managed relay (*.communities.buzz.xyz) on relay v0.2.0 breaks agent (buzz-acp) channel discovery — POST /query returns 404 with desktop v0.5.3

### Summary

The AI agent runtime (`buzz-acp` / `buzz-agent`) started from **Buzz Desktop v0.5.3** fails to start against a **managed community relay** (`*.communities.buzz.xyz`). The agent connects and authenticates successfully, then fails during channel discovery:

```
Error: channel discovery error: HTTP error: POST /query returned HTTP 404 Not Found
```

The relay reports **`"version":"0.2.0"`** in its NIP-11 document, while the desktop client is **0.5.3**. It looks like the managed relay is running a build that predates the HTTP `/query` channel-discovery endpoint the current agent expects, so the agent harness exits with status code 1.

### Environment

- **Desktop app:** Buzz Desktop `v0.5.3` (Windows x64, installer `Buzz_0.5.3_x64-setup_alpha-unsigned.exe`)
- **OS:** Windows 11 Pro
- **Agent runtime:** `buzz-agent` v0.1.0 via `buzz-acp`, `model=claude-opus-5`, `permission_mode=bypassPermissions`
- **Relay:** managed, `wss://.communities.buzz.xyz` (fronted by Cloudflare)
- **Relay NIP-11:** `software: https://github.com/block/buzz`, `version: 0.2.0`, `auth_required: true`, `restricted_writes: true`

### Steps to reproduce

1. Create a community via the app → it is provisioned on a managed `*.communities.buzz.xyz` relay.
2. Install Buzz Desktop v0.5.3 on Windows and complete profile setup.
3. Start/enable an agent (e.g. "Bumble") in the workspace.
4. Agent harness exits with status code 1.

### Log excerpt (`buzz-acp`)

```
INFO buzz_acp: buzz-acp starting: relay=wss://.communities.buzz.xyz agent_cmd=...\buzz-agent.exe mcp_cmd=...\buzz-dev-mcp.exe model=claude-opus-5 permission_mode=bypassPermissions ...
INFO buzz_acp: agent_pool_ready agents=10
INFO buzz_acp: connected to relay at wss://.communities.buzz.xyz
INFO buzz_acp: subscribed to membership notifications
INFO buzz_acp: owner resolved from BUZZ_AUTH_TAG:
INFO buzz_acp: agent owner:
INFO buzz_acp: relay observer enabled
Error: channel discovery error: HTTP error: POST /query returned HTTP 404 Not Found
```

### Additional observation

An unauthenticated `POST /query` against the relay returns **401 Unauthorized** (endpoint is auth-gated), while the agent's authenticated discovery call returns **404 Not Found** — consistent with the specific route/query shape used by the 0.5.3 agent not being implemented in the 0.2.0 relay build.

### Expected

Managed relays under `*.communities.buzz.xyz` should be on a build compatible with the current desktop/agent release, so agent channel discovery succeeds.

### Questions

- Are managed `*.communities.buzz.xyz` relays scheduled to be upgraded to match desktop v0.5.3?
- Is there a supported way for a community admin to trigger a relay upgrade, or a minimum relay version required for the agent runtime?