fix: Use D-Bus signature strings for Agent method annotations

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

main.py

@@ -33,37 +33,37 @@ class Agent(ServiceInterface):
         logging.info('Agent Released')
 
     @method()
-    def RequestPinCode(self, device: str) -> str:
+    def RequestPinCode(self, device: 'o') -> 's':
         logging.info(f"RequestPinCode for {device}, returning static PIN")
         return "0000"
 
     @method()
-    def RequestPasskey(self, device: str) -> int:
+    def RequestPasskey(self, device: 'o') -> 'u':
         logging.info(f"RequestPasskey for {device}")
         return 0
 
     @method()
-    def DisplayPasskey(self, device: str, passkey: int, entered: int):
+    def DisplayPasskey(self, device: 'o', passkey: 'u', entered: 'q'):
         logging.info(f"DisplayPasskey for {device}: {passkey}")
 
     @method()
-    def DisplayPinCode(self, device: str, pincode: str):
+    def DisplayPinCode(self, device: 'o', pincode: 's'):
         logging.info(f"DisplayPinCode for {device}: {pincode}")
 
     @method()
-    def RequestConfirmation(self, device: str, passkey: int):
+    def RequestConfirmation(self, device: 'o', passkey: 'u'):
         logging.info(f"RequestConfirmation for {device} with passkey {passkey}")
         # Automatically confirm and trust
         loop = asyncio.get_event_loop()
         loop.create_task(trust_and_connect_device(device))
 
     @method()
-    def RequestAuthorization(self, device: str):
+    def RequestAuthorization(self, device: 'o'):
         logging.info(f"RequestAuthorization for {device}")
         pass
 
     @method()
-    def AuthorizeService(self, device: str, uuid: str):
+    def AuthorizeService(self, device: 'o', uuid: 's'):
         logging.info(f"AuthorizeService for {device} with uuid {uuid}")
         pass