fix: derive wifi interface dynamically from gateway info instead of detecting at startup

Remove static wifi_interface/ethernet_interface fields from RpcContextSeed. Instead, look up
the wifi interface from the DB (populated by gateway sync) and check ethernet connectivity
by querying gateway entries. This ensures the wifi manager always uses the correct interface
even if network devices change after boot.

core/src/db/model/public.rs

@@ -98,7 +98,7 @@ impl Public {
                         port_forwards: BTreeSet::new(),
                     },
                     wifi: WifiInfo {
-                        enabled: true,
+                        enabled: false,
                         ..Default::default()
                     },
                     gateways: OrdMap::new(),
@@ -378,7 +378,7 @@ pub struct ServerStatus {
 #[ts(export)]
 pub struct WifiInfo {
     pub enabled: bool,
-    pub interface: Option<String>,
+    pub interface: Option<GatewayId>,
     pub ssids: BTreeSet<String>,
     pub selected: Option<String>,
     #[ts(type = "string | null")]