Add Birdcage TUI: 5-screen Textual interface for Carryout G2

F1 Position (compass rose, motor control, sparklines),
F2 Signal (RSSI gauge with sub-char precision, DVB/ADC sparklines, LNA toggle),
F3 Scan (AZ/EL grid sweep with heatmap and CSV export),
F4 System (NVS table, A3981 diagnostics, motor dynamics),
F5 Console (raw serial terminal with prompt detection and safety gates).

Includes SerialBridge (thread-safe protocol wrapper), DemoDevice
(synthetic simulation for --demo mode), dark RF theme with rounded
borders and teal accents, and send_raw() on CarryoutG2Protocol.

src/birdcage/protocol.py

@@ -392,6 +392,10 @@ class CarryoutG2Protocol(FirmwareProtocol):
 
         raise ValueError(f"Could not parse RSSI from: {response!r}")
 
+    def send_raw(self, cmd: str) -> str:
+        """Send arbitrary command, return raw prompt-terminated response."""
+        return self._send(cmd)
+
     def quit_submenu(self) -> None:
         """Exit current submenu and return to parent."""
         self._send("q")