chore(compiler): Enable strict property access TS compiler flag. (#6255)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/cli/src/ui/App.tsx

@@ -1089,7 +1089,7 @@ const App = ({ config, settings, startupWarnings = [], version }: AppProps) => {
                 alignItems={isNarrow ? 'flex-start' : 'center'}
               >
                 <Box>
-                  {process.env.GEMINI_SYSTEM_MD && (
+                  {process.env['GEMINI_SYSTEM_MD'] && (
                     <Text color={Colors.AccentRed}>|⌐■_■| </Text>
                   )}
                   {ctrlCPressedOnce ? (