Add Ko-fi support button to website CTA and footer

Places a branded Ko-fi button (#FF5E5B) with coffee cup emoji alongside
the download button in the CTA section, and as a compact button in the
footer, both linking to https://ko-fi.com/vaultsoft.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Initial release — PulseMonitor v1.0.0