Add Hugo link page with Sveltia CMS admin

Content lives in data/profile.yaml and is edited as structured fields through Sveltia at /admin/, so the page is never hand-written HTML. The CMS bundle is vendored at a pinned version instead of loaded from unpkg, and the admin assets ship with the built site, so hosting and builds stay self-contained. PKCE sign-in activates once a Gitea OAuth application client ID is added to static/admin/config.yml.

assets/icons/envelope.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-envelope" viewBox="0 0 16 16">
+  <path d="M0 4a2 2 0 0 1 2-2h12a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H2a2 2 0 0 1-2-2zm2-1a1 1 0 0 0-1 1v.217l7 4.2 7-4.2V4a1 1 0 0 0-1-1zm13 2.383-4.708 2.825L15 11.105zm-.034 6.876-5.64-3.471L8 9.583l-1.326-.795-5.64 3.47A1 1 0 0 0 2 13h12a1 1 0 0 0 .966-.741M1 11.105l4.708-2.897L1 5.383z"/>
+</svg>