Shared-compute node silently dropped when home relay not in MESH_LLM_DEFAULT_RELAYS #6724

Describe the bug
A healthy mesh-llm node is silently dropped by default, due to the MESH_LLM_DEFAULT_RELAYS constant listing only 2 relays.

Steps to reproduce

1. Run a headless mesh-llm serve (relays enabled, i.e. no
   --disable-iroh-relays) that homes onto use1-1 or euc1-1 — confirm via
   the endpoint token in GET :<console>/api/status (decode the base64url
   token; look at the Relay addr).
2. Admit that node's npub to a closed relay and connect a stock Buzz desktop
   (Default mode, BUZZ_MESH_IROH_RELAYS unset) as an admitted member.
3. The desktop discovers the node's status note but never lists it as an
   available shared-compute target; agent mentions fail with "no live member is
   serving this model."

Expected behavior
It should allow the default iroh relays by default.

Version and platform

• Buzz version: 0.5.18 (client), mesh-llm v0.75.1 (compute server)
• OS: macOS 27.0 build 26A5406e (client), Gentoo Linux w/kernel 6.18.39 (compute server)