Add Datenschutzerklärung, two blog posts, and a /uses colophon

- datenschutz.astro: DSGVO privacy policy (server logfiles, Hetzner as
  Auftragsverarbeiter per Art. 28, cookieless Umami, self-hosted fonts,
  data-subject rights, supervisory-authority complaint).
- consts.ts: extract shared LEGAL entity data; Impressum now reads from it.
- blog: "Why my calendar app has no internet permission" and
  "Open standards as a constraint, not a checkbox".
- uses.astro: colophon of the site stack, Floret apps, and self-hosted infra.
- Footer: add Uses + Datenschutz links alongside Impressum.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/Footer.astro

@@ -6,7 +6,10 @@ const year = new Date().getFullYear();
 
 <footer class="site-footer">
   <div class="site-footer__inner">
-    <p>© {year} {SITE.author} · <a href="/impressum">Impressum</a></p>
+    <p>
+      © {year} {SITE.author} · <a href="/uses">Uses</a> ·
+      <a href="/impressum">Impressum</a> · <a href="/datenschutz">Datenschutz</a>
+    </p>
     {
       SOCIALS.length > 0 && (
         <nav aria-label="Social" class="socials">