feat: US-014 - Responsive verification and fixes across breakpoints

- Fix grid overflow at mobile: add minWidth:0 + overflow:hidden to Card
- Scale ParentSection h2 responsively (1.5rem mobile → 2.4rem desktop)
- Make KPI grid single-column below 480px, 2-column above
- Fix SubNav alignment: left-aligned on mobile, centered on md+
- Fix SubNav tileIds to match restructured dashboard sections
- Add data-tile-id anchors to experience/skills/education subsections

src/components/ParentSection.tsx

@@ -12,8 +12,8 @@ export function ParentSection({ title, children, className, tileId }: ParentSect
   return (
     <Card full className={className} tileId={tileId}>
       <h2
+        className="text-[1.5rem] sm:text-[1.8rem] md:text-[2rem] lg:text-[2.4rem]"
         style={{
-          fontSize: '2.4rem',
           fontWeight: 700,
           color: 'var(--text-primary)',
           lineHeight: 1.1,