Display build date in UI, injected during CI build

.gitea/workflows/build-publish.yaml

@@ -33,6 +33,8 @@ jobs:
       - name: Build
         run: |
           ARCH=$(uname -m)
+          BUILD_DATE=$(TZ=Pacific/Auckland date +"%Y-%m-%d %H:%M %Z")
+          sed -i "s|__BUILD_DATE__|${BUILD_DATE}|g" ./app/app.py
           docker build --provenance=false -t gitea.jde.nz/public/infmap:latest-${ARCH} ./app
 
       - name: Publish