fix(ci): use --load + docker push instead of --push for HTTP registry

docker build --push uses buildkit's internal push which connects directly
to the registry over HTTPS, bypassing the Podman daemon. Since the Gitea
registry is HTTP-only, this fails with "server gave HTTP response to HTTPS client".

Switch to --load (exports image into Podman daemon) then docker push (goes
through the daemon which has insecure=true in registries.conf → uses HTTP).
Tag the SHA variant with docker tag before pushing both.

Also:
- Add NEXT_PUBLIC_CLOUDINARY_CLOUD_NAME ARG/ENV to admin Dockerfile
- Add STAGING_ prefix note to both Dockerfiles builder stage
- Add STAGING_NEXT_PUBLIC_CLOUDINARY_CLOUD_NAME to workflow env and
  pass it as --build-arg for admin builds only

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

.gitea/workflows/deploy-staging.yml

@@ -101,9 +101,11 @@ jobs:
           echo "{\"auths\":{\"${REGISTRY_HOST}\":{\"auth\":\"${AUTH}\"}}}" > ~/.docker/config.json
 
       - name: Build & push ${{ matrix.app }}
-        # Uses --push to push directly during build, which avoids the "No output
-        # specified with docker-container driver" warning that appears when using
-        # a separate docker push step without --load. (see: troubleshooting #5)
+        # --push bypasses the Podman daemon and uses buildkit's internal HTTPS push,
+        # which fails for HTTP-only registries. Instead:
+        #   1. --load loads the image into the Podman daemon after build
+        #   2. docker push goes through the daemon, which has insecure=true in
+        #      registries.conf and correctly uses HTTP. (see: troubleshooting #7, #12)
         #
         # Each app has its own Clerk instance so the publishable key differs.
         # NEXT_PUBLIC_* vars must be baked in at build time — Next.js prerender
@@ -126,9 +128,8 @@ jobs:
               --build-arg NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY="$CLERK_KEY" \
               --build-arg NEXT_PUBLIC_CONVEX_URL="$NEXT_PUBLIC_CONVEX_URL" \
               --build-arg NEXT_PUBLIC_CLOUDINARY_CLOUD_NAME="$NEXT_PUBLIC_CLOUDINARY_CLOUD_NAME" \
+              --load \
               -t "${IMAGE}:staging" \
-              -t "${IMAGE}:sha-${SHORT_SHA}" \
-              --push \
               ./out
           else
             CLERK_KEY="$STOREFRONT_CLERK_KEY"
@@ -136,12 +137,15 @@ jobs:
               -f apps/storefront/Dockerfile \
               --build-arg NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY="$CLERK_KEY" \
               --build-arg NEXT_PUBLIC_CONVEX_URL="$NEXT_PUBLIC_CONVEX_URL" \
+              --load \
               -t "${IMAGE}:staging" \
-              -t "${IMAGE}:sha-${SHORT_SHA}" \
-              --push \
               ./out
           fi
 
+          docker tag "${IMAGE}:staging" "${IMAGE}:sha-${SHORT_SHA}"
+          docker push "${IMAGE}:staging"
+          docker push "${IMAGE}:sha-${SHORT_SHA}"
+
   # ── 3. Deploy ───────────────────────────────────────────────────────────────
 
   deploy: