Fix GrampsWeb subpath: patch <base href> at container startup (STI-93)

The GrampsWeb SPA has <base href="/"> hardcoded at build time, causing
assets to load from / instead of /ahnenforschung/ when behind a reverse
proxy. Instead of relying on nginx sub_filter (which may not be available),
patch the HTML at container startup via GRAMPSWEB_SUBPATH env var.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deploy-production/docker-compose.prod.yml

@@ -128,6 +128,22 @@ services:
       - GRAMPSWEB_CELERY_CONFIG__result_backend=redis://redis:6379/0
       - GRAMPSWEB_RATELIMIT_STORAGE_URI=redis://redis:6379/1
       - GRAMPSWEB_NEW_DB_BACKEND=sqlite
+      - GRAMPSWEB_SUBPATH=${GRAMPSWEB_SUBPATH:-/ahnenforschung}
+    command:
+      - sh
+      - -c
+      - |
+        if [ -n "$$GRAMPSWEB_SUBPATH" ] && [ "$$GRAMPSWEB_SUBPATH" != "/" ]; then
+          SUBPATH="$$GRAMPSWEB_SUBPATH"
+          case "$$SUBPATH" in */) ;; *) SUBPATH="$${SUBPATH}/" ;; esac
+          sed -i "s|<base href=\"/\">|<base href=\"$$SUBPATH\">|g" \
+            /app/src/gramps_webapi/static/index.html \
+            /app/static/index.html 2>/dev/null || true
+          echo "Patched <base href> to $$SUBPATH"
+        fi
+        exec gunicorn -w $${GUNICORN_NUM_WORKERS:-8} -b 0.0.0.0:5000 \
+          gramps_webapi.wsgi:app --timeout $${GUNICORN_TIMEOUT:-120} \
+          --limit-request-line 8190
     volumes:
       - gramps_data:/app/data
     depends_on: