feat: add font size controls to mobile terminal header and fix auto-hide space reclamation

- TerminalComponent: expose changeFontSize via onTerminalReady callback
- MobileTerminalWrapper: pass changeFontSize to header
- MobileTerminalHeader: add A- and A+ font size buttons
- CSS: collapse header height/padding/margin/border when hidden to reclaim space

apps/web/src/components/mobile-terminal-header.tsx

@@ -6,6 +6,7 @@ interface MobileTerminalHeaderProps {
   onBack?: () => void;
   onMenuToggle?: () => void;
   onClose?: () => void;
+  onFontSizeChange?: (delta: number) => void;
   isVisible: boolean;
   connectionStatus?: "connecting" | "connected" | "disconnected" | "error";
 }
@@ -15,6 +16,7 @@ export const MobileTerminalHeader: React.FC<MobileTerminalHeaderProps> = ({
   onBack,
   onMenuToggle,
   onClose,
+  onFontSizeChange,
   isVisible,
   connectionStatus = "connecting",
 }) => {
@@ -56,6 +58,26 @@ export const MobileTerminalHeader: React.FC<MobileTerminalHeaderProps> = ({
       </div>
 
       <div className="mobile-terminal-header-right">
+        {onFontSizeChange && (
+          <>
+            <button
+              className="mobile-terminal-header-button"
+              onClick={() => onFontSizeChange(-1)}
+              type="button"
+              aria-label="Decrease font size"
+            >
+              <span style={{ fontSize: "0.75rem" }}>A-</span>
+            </button>
+            <button
+              className="mobile-terminal-header-button"
+              onClick={() => onFontSizeChange(1)}
+              type="button"
+              aria-label="Increase font size"
+            >
+              <span style={{ fontSize: "1rem" }}>A+</span>
+            </button>
+          </>
+        )}
         {onClose && (
           <button
             className="mobile-terminal-header-button"