ci(release): wire IMPORT_HOST_DIR=/srv/familienarchiv-production/import

Mirrors the staging change. The host directory does not yet exist on
the production server — first production release that consumes this
will create an empty bind source via Docker's auto-create behaviour;
mass import then reports "no spreadsheet found" until an operator
pre-stages a payload there.

Addresses Tobias's review on #526.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -71,6 +71,7 @@ jobs:
           MAIL_SMTP_AUTH=true
           MAIL_STARTTLS_ENABLE=true
           APP_MAIL_FROM=noreply@raddatz.cloud
+          IMPORT_HOST_DIR=/srv/familienarchiv-production/import
           EOF
 
       - name: Build images