Fix CPU reporting: MikroTik uses 0x80|pct encoding, add CPU to CSV

- MikroTik encodes CPU as 0x80 | percentage (high bit flag)
- Deserialize: mask with 0x7F and cap at 100
- Serialize: set high bit (0x80 | cpu) to match MikroTik format
- CSV now includes local_cpu_pct and remote_cpu_pct columns
- Both client and server write CPU to CSV

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/server.rs

@@ -357,7 +357,8 @@ async fn handle_client(
     if crate::csv_output::is_enabled() {
         crate::csv_output::write_result(
             &peer.ip().to_string(), peer.port(), proto_str, dir_str,
-            intervals as u64, total_tx, total_rx, total_lost, auth_type,
+            intervals as u64, total_tx, total_rx, total_lost,
+            crate::cpu::get(), 0, auth_type,
         );
     }
     result.map(|_| ())