fix: remove viewport-based font size calculation causing jump on mobile

The calculateFontSize() function was overriding the font size on mobile
based on viewport width (vw/25), causing the terminal to display at ~15px
while the internal state was 8px. When pressing A-, it would jump from
15px to 7px. Now it respects the actual fontSize state consistently.

Quality gates: TypeScript check passed, production build successful

apps/web/src/components/terminal.tsx

@@ -64,11 +64,8 @@ export const TerminalComponent: React.FC<TerminalProps> = ({
   const isUnmountingRef = useRef(false);
 
   const calculateFontSize = useCallback(() => {
-    if (!isMobile) return fontSize;
-    const vw = window.innerWidth;
-    const calculated = Math.max(MIN_FONT_SIZE, Math.min(MAX_FONT_SIZE, vw / 25));
-    return Math.round(calculated);
-  }, [isMobile, fontSize]);
+    return fontSize;
+  }, [fontSize]);
 
   const connectWebSocket = useCallback(() => {
     const apiUrl = import.meta.env.VITE_API_BASE_URL || "";