Revert termios modifications - may cause serial corruption

The termios changes (disabling ECHO, ICANON) may be causing
serial data corruption (G1 -> O1). Main branch doesn't have
these modifications and works fine.

The FluidNC echo is handled in pattern_manager.py by ignoring
echoed G-code commands, so termios-level echo suppression
is not needed.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

modules/connection/connection_manager.py

@@ -74,23 +74,6 @@ class SerialConnection(BaseConnection):
         self.lock = threading.RLock()
         logger.info(f'Connecting to Serial port {port}')
         self.ser = serial.Serial(port, baudrate, timeout=timeout)
-
-        # Disable serial echo - critical for Pi 3B+ where ttyAMA0 may have echo enabled
-        # Without this, sent commands are echoed back and the motion thread never sees 'ok'
-        try:
-            import termios
-            # Get current terminal attributes
-            attrs = termios.tcgetattr(self.ser.fileno())
-            # Disable echo (ECHO) and other local flags that could cause issues
-            attrs[3] = attrs[3] & ~termios.ECHO & ~termios.ECHOE & ~termios.ECHOK & ~termios.ECHONL
-            # Set raw mode for input (no special processing)
-            attrs[3] = attrs[3] & ~termios.ICANON
-            # Apply the new attributes immediately
-            termios.tcsetattr(self.ser.fileno(), termios.TCSANOW, attrs)
-            logger.info(f'Serial echo disabled on {port}')
-        except Exception as e:
-            logger.warning(f'Could not disable serial echo (may not be needed): {e}')
-
         state.port = port
         logger.info(f'Connected to Serial port {port}')