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>

compose.yml

@@ -198,7 +198,7 @@ services:
       - GRAMPSWEB_ADMIN_EMAIL=${GRAMPSWEB_ADMIN_EMAIL:-admin@localhost}
       - GRAMPSWEB_ADMIN_PASSWORD=${GRAMPSWEB_ADMIN_PASSWORD:-gramps_dev_password}
       - GRAMPSWEB_TREE=${GRAMPSWEB_TREE:-Stiftung}
-      - GRAMPSWEB_BASE_URL=${GRAMPSWEB_BASE_URL:-https://vhtv-stiftung.de/ahnenforschung}
+      - GRAMPSWEB_BASE_URL=${GRAMPSWEB_BASE_URL:-https://ahnenforschung.vhtv-stiftung.de}
       - GRAMPSWEB_CELERY_CONFIG__broker_url=redis://redis:6379/0
       - GRAMPSWEB_CELERY_CONFIG__result_backend=redis://redis:6379/0
       - GRAMPSWEB_RATELIMIT_STORAGE_URI=redis://redis:6379/1
@@ -207,7 +207,7 @@ services:
       - sh
       - -c
       - |
-        # All subpath rewriting is handled by nginx sub_filter — no container patching needed.
+        # GrampsWeb runs on its own subdomain — no subpath rewriting needed.
         echo "[grampsweb] Ensuring admin user exists ..."
         python3 << 'PYEOF' 2>&1 | grep -v Gtk
         from gramps_webapi.app import create_app