fix: build base image on every push so prop-base:latest is always available

prop-base:latest is required by the production Dockerfile's final stage
but was only built when Dockerfile.base changed. The registry can GC
unused images. Remove paths filter so the image is always kept fresh.

.forgejo/workflows/build-base.yaml

@@ -4,9 +4,6 @@ on:
   push:
     branches:
       - main
-    paths:
-      - 'Dockerfile.base'
-      - '.forgejo/workflows/build-base.yaml'
   schedule:
     - cron: '0 6 * * 0'
   workflow_dispatch: