feat(server): unify WireGuard into the shared server transport pipeline

rust/src/network.rs

@@ -86,6 +86,16 @@ impl IpPool {
         client_id
     }
 
+    /// Reserve a specific IP for a client (e.g., WireGuard static IP from allowed_ips).
+    pub fn reserve(&mut self, ip: Ipv4Addr, client_id: &str) -> Result<()> {
+        if self.allocated.contains_key(&ip) {
+            anyhow::bail!("IP {} is already allocated", ip);
+        }
+        self.allocated.insert(ip, client_id.to_string());
+        info!("Reserved IP {} for client {}", ip, client_id);
+        Ok(())
+    }
+
     /// Number of currently allocated IPs.
     pub fn allocated_count(&self) -> usize {
         self.allocated.len()