build: build Go images from the repo root for the shared module

Also pins the explicit shared require in both go.mod files. `go mod tidy`
in workspace mode drops it, which breaks the Docker build where no
workspace exists.

.gitea/workflows/server-deploy.yml

@@ -24,7 +24,8 @@ jobs:
             - name: Build and push server image
               run: |
                   IMAGE="${{ vars.DOCKER_HOST }}/${{ github.repository_owner }}/vantage/server:latest"
-                  docker build -t "$IMAGE" -f server/Dockerfile server/
+                  # Root context: server depends on the shared module.
+                  docker build -t "$IMAGE" -f server/Dockerfile .
                   docker push "$IMAGE"
 
             - name: Build and push web image
@@ -49,5 +50,6 @@ jobs:
             - name: Build and push sitesvc image
               run: |
                   IMAGE="${{ vars.DOCKER_HOST }}/${{ github.repository_owner }}/vantage/sitesvc:latest"
-                  docker build -t "$IMAGE" -f sitesvc/Dockerfile sitesvc/
+                  # Root context: sitesvc depends on the shared module.
+                  docker build -t "$IMAGE" -f sitesvc/Dockerfile .
                   docker push "$IMAGE"