fix(docker): use pre-built frontend assets instead of rebuilding in container (#558)

The frontend-builder stage failed on Alpine because svelma could not
resolve bulma Sass imports. The CI pipeline already pre-builds the
frontend on ubuntu-22.04 and passes it as an artifact in the Docker
build context at desktop/dist/. Replace the Node.js Alpine build stage
with a scratch stage that copies pre-built assets directly.

This also prepares for the desktop being moved to a separate repository,
where in-container frontend builds would no longer be possible.

Fixes Docker 20.04 build failure in release workflow.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: AlexMikhalev

.github/workflows/docker-multiarch.yml

@@ -209,7 +209,6 @@ jobs:
           build-args: |
             UBUNTU_VERSION=${{ matrix.ubuntu-version }}
             RUST_VERSION=1.92.0
-            NODE_VERSION=20
           cache-from: type=gha
           cache-to: type=gha,mode=max
           provenance: false
@@ -229,7 +228,6 @@ jobs:
           build-args: |
             UBUNTU_VERSION=${{ matrix.ubuntu-version }}
             RUST_VERSION=1.92.0
-            NODE_VERSION=20
           cache-from: type=gha
           provenance: false
           sbom: false

docker/Dockerfile.multiarch

@@ -3,24 +3,16 @@
 
 ARG UBUNTU_VERSION=22.04
 ARG RUST_VERSION=1.85.0
-ARG NODE_VERSION=20
 
 # ================================
-# Frontend Build Stage
+# Frontend Assets Stage
 # ================================
-FROM --platform=$BUILDPLATFORM node:${NODE_VERSION}-alpine AS frontend-builder
-
-WORKDIR /app
-# Copy package files - yarn.lock is optional
-COPY desktop/package*.json ./
-COPY desktop/yarn.lock* ./
-RUN yarn install --frozen-lockfile --network-timeout 300000
-
-COPY desktop ./
-RUN yarn run build
-
-# Verify frontend build
-RUN ls -la dist/ && test -f dist/index.html
+# Desktop has been moved to a separate repository.
+# The CI pipeline (docker-multiarch.yml) pre-builds the frontend
+# and places the dist/ output in the Docker build context at desktop/dist/.
+# We simply copy those pre-built assets here.
+FROM scratch AS frontend-assets
+COPY desktop/dist/ /dist/
 
 # ================================
 # Rust Build Stage
@@ -124,7 +116,7 @@ RUN . /root/.profile && \
 # Copy source code
 COPY crates ./crates
 COPY terraphim_server ./terraphim_server
-COPY --from=frontend-builder /app/dist ./terraphim_server/dist
+COPY --from=frontend-assets /dist ./terraphim_server/dist
 
 # Build the application
 RUN . /root/.profile && \