Enable pageview tracking when VITE_UMAMI_WEBSITE_ID is set at frontend
build time (Forgejo secret + deploy workflow), with SPA route updates
and no script in local dev. Document setup in docs/umami-analytics.md,
extend integritetspolicy, and add admin Webbstatistik link in prod builds.
Co-authored-by: Cursor <cursoragent@cursor.com>
