feat(nodes): mesh awareness + node detail page

- agent reports tailscale/netbird/zerotier/wireguard interface IPs at
  register (authoritative — absent interfaces clear stored state)
- backend stores under node_agents.metadata.mesh, merged on re-register
- node detail page shows mesh addresses under the primary IP

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

docs/api/openapi.yaml

@@ -9130,6 +9130,11 @@ components:
         auth_token:
           type: string
           description: May also be sent via the X-Agent-Token header
+        mesh:
+          type: object
+          additionalProperties:
+            type: string
+          description: Overlay-network interface IPs (tailscale/netbird/zerotier/wireguard). Stored under agent metadata.mesh; authoritative — send an empty object when no mesh interfaces exist.
 
     AgentHeartbeat:
       type: object