feat(stockholm): add Dockerfile.stockholm and Makefile targets for frontend prep

Dockerfile.stockholm clones github.com/krahl/soundcork-stockholm-app at build
time and installs the required tools (prettier, patch, unzip, jq). No pre-built
image is published upstream, so users must run `make build-stockholm-image` once
before `make prepare-stockholm`.

`make prepare-stockholm` runs the upstream entrypoint logic (extract zip,
run prettier, apply patches) via a volume-mounted docker run, stopping before
`exec java` so we only collect the processed stockholm/ output. The Go service
then serves that directory directly with no patching required at runtime.

Prerequisites: Docker with internet access, and stockholm_zip/stockholm.zip
(Stockholm source zip placed manually — tracked directory, zip gitignored).

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

.gitignore

@@ -98,3 +98,9 @@ pids
 
 # dotenv environment variables file (but keep .env.example)
 !.env.example
+
+# Stockholm frontend — generated by `make prepare-stockholm`, not committed
+stockholm/
+
+# Stockholm source zip — large binary, place manually at stockholm_zip/stockholm.zip
+stockholm_zip/*.zip

Dockerfile.stockholm

@@ -0,0 +1,40 @@
+# Dockerfile.stockholm — builds the Stockholm frontend preparation image.
+#
+# This image clones krahl/soundcork-stockholm-app, installs the required tools
+# (prettier, patch, unzip, jq), and is used exclusively to run the entrypoint
+# preparation step that extracts and patches the Stockholm frontend.
+#
+# Java is NOT included — we stop before `exec java`.
+#
+# Usage (see Makefile targets build-stockholm-image / prepare-stockholm):
+#
+#   docker build --build-arg STOCKHOLM_APP_REF=main \
+#       -f Dockerfile.stockholm -t soundcork-stockholm-app .
+#
+#   docker run --rm \
+#       -v "$PWD/stockholm_zip:/app/stockholm_zip:ro" \
+#       -v "$PWD/stockholm:/app/stockholm" \
+#       --entrypoint bash soundcork-stockholm-app \
+#       -c 'awk "/^exec java/{exit} {print}" /app/docker-entrypoint.sh | bash'
+
+FROM debian:bookworm-slim
+
+ARG STOCKHOLM_APP_REF=main
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        ca-certificates \
+        git \
+        jq \
+        unzip \
+        nodejs \
+        npm \
+        patch && \
+    rm -rf /var/lib/apt/lists/*
+
+RUN npm install -g prettier@3.8.3 && npm cache clean --force
+
+RUN git clone --depth 1 --branch "${STOCKHOLM_APP_REF}" \
+    https://github.com/krahl/soundcork-stockholm-app /app
+
+WORKDIR /app

Makefile

@@ -1,4 +1,4 @@
-.PHONY: all build build-cli test test-coverage check fmt vet lint clean dev help screenshots
+.PHONY: all build build-cli test test-coverage check fmt vet lint clean dev help screenshots build-stockholm-image prepare-stockholm
 
 # Go parameters
 GOCMD=go
@@ -31,6 +31,13 @@ BUILD_DIR=./build
 # Build flags: strip debug info/DWARF for smaller binaries, remove local paths for reproducibility
 BUILDFLAGS=-trimpath -ldflags="-s -w"
 
+# Stockholm frontend preparation (see Dockerfile.stockholm and docs/stockholm-port-guide.md)
+# STOCKHOLM_APP_REF can be overridden to pin a specific commit: make build-stockholm-image STOCKHOLM_APP_REF=<sha>
+STOCKHOLM_IMAGE   ?= soundcork-stockholm-app
+STOCKHOLM_APP_REF ?= main
+STOCKHOLM_ZIP_DIR ?= $(CURDIR)/stockholm_zip
+STOCKHOLM_DIR     ?= $(CURDIR)/stockholm
+
 all: check build
 
 build: build-cli build-service build-web build-examples build-favicon-gen build-backup
@@ -329,6 +336,34 @@ docker-build:
 	@echo "Building Docker image..."
 	docker build --target soundtouch-service -t soundtouch-service .
 
+# Stockholm frontend preparation.
+# Requires: Docker, internet access (clones github.com/krahl/soundcork-stockholm-app).
+# No pre-built image is published; the image must be built locally before running prepare-stockholm.
+build-stockholm-image:
+	@echo "Building Stockholm preparation image (clones upstream, installs prettier/patch)..."
+	docker build \
+		--build-arg STOCKHOLM_APP_REF=$(STOCKHOLM_APP_REF) \
+		-f Dockerfile.stockholm \
+		-t $(STOCKHOLM_IMAGE) \
+		.
+
+# Extracts and patches the Stockholm frontend using the upstream container image.
+# Requires: build-stockholm-image to have been run, and stockholm_zip/stockholm.zip to be present.
+# The resulting stockholm/ directory is used by the soundtouch-service at runtime.
+prepare-stockholm:
+	@mkdir -p "$(STOCKHOLM_DIR)"
+	@[ -f "$(STOCKHOLM_ZIP_DIR)/stockholm.zip" ] || { \
+		echo "Error: $(STOCKHOLM_ZIP_DIR)/stockholm.zip not found."; \
+		echo "Download the Stockholm zip and place it at stockholm_zip/stockholm.zip first."; \
+		exit 1; }
+	docker run --rm \
+		-v "$(STOCKHOLM_ZIP_DIR):/app/stockholm_zip:ro" \
+		-v "$(STOCKHOLM_DIR):/app/stockholm" \
+		--entrypoint bash \
+		$(STOCKHOLM_IMAGE) \
+		-c 'awk "/^exec java/{exit} {print}" /app/docker-entrypoint.sh | bash'
+	@echo "Stockholm frontend prepared at $(STOCKHOLM_DIR)"
+
 docker-run-host:
 	@echo "Running Docker container..."
 	@echo "Note: --network host is used for discovery (Linux only). For macOS/Windows use port mapping."
@@ -386,6 +421,9 @@ help:
 	@echo "  docker-build  - Build Docker image"
 	@echo "  docker-run-host  - Run container with host networking (Linux discovery)"
 	@echo "  docker-run-ports - Run container with port mapping (macOS/Windows/No discovery)"
+	@echo "  build-stockholm-image - Build Stockholm prep image (requires Docker + internet)"
+	@echo "  prepare-stockholm     - Extract and patch Stockholm frontend (requires build-stockholm-image"
+	@echo "                          and stockholm_zip/stockholm.zip; see docs/stockholm-port-guide.md)"
 	@echo "  help          - Show this help message"
 	@echo ""
 	@echo "Examples:"