fix: stats links use same origin, move theme toggle to footer
- stats/dashboard links use /dashboard.html (same origin) instead of
going through backend redirect to dead leaflet-search.pages.dev URL
- theme toggle moved from cramped header to bottom of page where it
doesn't clutter the title line
- dashboard "back" and title links use relative paths (same origin)
- backend DASHBOARD_URL default updated to pub-search.waow.tech
- localStorage theme now shared between search and stats pages
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>