fix(a11y): improve footer section heading semantics

While reviewing the Footer component for accessibility refinements, I noticed that a

element is currently nested inside a Button component in:

frontend/src/components/Footer.tsx

Since Button renders a native element, this results in a heading being placed inside an interactive element. Although this does not affect visual rendering, it may impact document outline structure and screen reader interpretation.

Proposed minimal adjustment:
- Replace the

with a styled to preserve visual appearance
OR
- Adjust structure to maintain heading semantics without nesting inside

This would not modify behavior or layout — only improve semantic correctness and accessibility compliance.

Happy to implement this following project conventions if aligned with maintainers.