Switch GrampsWeb from subpath to subdomain ahnenforschung.vhtv-stiftung.de (STI-91)

The subpath approach (/ahnenforschung/) required ~15 nginx sub_filter
rules to rewrite JS/CSS/HTML paths, causing persistent issues with
font loading, Service Worker, and API routes. GrampsWeb is not designed
for subpath deployment.

Switch to dedicated subdomain where GrampsWeb runs on root /:
- nginx.conf: remove all sub_filter rules, add clean subdomain server block
- base.html: update sidebar link to subdomain URL
- compose.yml: update GRAMPSWEB_BASE_URL default
- env-template.txt: update BASE_URL reference

After deploy: run certbot for ahnenforschung.vhtv-stiftung.de SSL cert,
update .env GRAMPSWEB_BASE_URL, restart containers.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

env-template.txt

@@ -64,7 +64,7 @@ GRAMPSWEB_SECRET_KEY=your-grampsweb-secret-key-here
 GRAMPSWEB_ADMIN_EMAIL=admin@vhtv-stiftung.de
 GRAMPSWEB_ADMIN_PASSWORD=your-grampsweb-admin-password-here
 GRAMPSWEB_TREE=Stiftung
-# Full external URL including subpath (used by GrampsWeb for email links, OIDC, etc.)
-GRAMPSWEB_BASE_URL=https://vhtv-stiftung.de/ahnenforschung
+# Full external URL (used by GrampsWeb for email links, OIDC, etc.)
+GRAMPSWEB_BASE_URL=https://ahnenforschung.vhtv-stiftung.de