Split Docker config for dev/prod and fix arch-agnostic builds

- Dockerfile: use --platform=$BUILDPLATFORM + ARG TARGETARCH instead of
  hardcoded GOARCH=arm64, enabling cross-compilation and native builds
  on both arm64 (M1) and amd64 (prod server)
- docker-compose.yml: rewrite for Docker Swarm — image refs, deploy
  sections, overlay network, no container_name/depends_on conditions,
  DB/Redis ports not exposed externally
- docker-compose.dev.yml: rewrite as self-contained dev compose with
  build targets, container_name, depends_on, dev-safe defaults
- Makefile: switch to docker compose v2, point dev targets at
  docker-compose.dev.yml, add docker-build-prod target
- Delete stale docker/Dockerfile (Go 1.21) and docker/docker-compose.yml

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

Makefile

@@ -3,7 +3,6 @@
 # Binary names
 API_BINARY=casera-api
 WORKER_BINARY=casera-worker
-ADMIN_BINARY=casera-admin
 
 # Build flags
 LDFLAGS=-ldflags "-s -w"
@@ -24,12 +23,8 @@ build:
 build-worker:
 	go build $(LDFLAGS) -o bin/$(WORKER_BINARY) ./cmd/worker
 
-# Build the admin binary
-build-admin:
-	go build $(LDFLAGS) -o bin/$(ADMIN_BINARY) ./cmd/admin
-
 # Build all binaries
-build-all: build build-worker build-admin
+build-all: build build-worker
 
 # Run the API server
 run:
@@ -39,10 +34,6 @@ run:
 run-worker:
 	go run ./cmd/worker
 
-# Run the admin
-run-admin:
-	go run ./cmd/admin
-
 # Run tests
 test:
 	go test -v -race -cover ./...
@@ -73,24 +64,30 @@ fmt:
 vet:
 	go vet ./...
 
-# Docker commands
+# Docker commands (dev — uses docker-compose.dev.yml)
 docker-build:
-	docker-compose build
+	docker compose -f docker-compose.dev.yml build
 
 docker-up:
-	docker-compose up -d
+	docker compose -f docker-compose.dev.yml up -d
 
 docker-down:
-	docker-compose down
+	docker compose -f docker-compose.dev.yml down
 
 docker-logs:
-	docker-compose logs -f
+	docker compose -f docker-compose.dev.yml logs -f
 
 docker-dev:
-	docker-compose -f docker-compose.yml -f docker-compose.dev.yml up --build
+	docker compose -f docker-compose.dev.yml up --build
 
 docker-restart:
-	docker-compose down && docker-compose up -d
+	docker compose -f docker-compose.dev.yml down && docker compose -f docker-compose.dev.yml up -d
+
+# Docker commands (prod — builds production images)
+docker-build-prod:
+	docker build --target api -t $${REGISTRY:-ghcr.io/treytartt}/casera-api:$${TAG:-latest} .
+	docker build --target worker -t $${REGISTRY:-ghcr.io/treytartt}/casera-worker:$${TAG:-latest} .
+	docker build --target admin -t $${REGISTRY:-ghcr.io/treytartt}/casera-admin:$${TAG:-latest} .
 
 # Database migrations
 migrate-up:
@@ -116,13 +113,12 @@ help:
 	@echo "Build:"
 	@echo "  deps          - Install dependencies"
 	@echo "  build         - Build API binary"
-	@echo "  build-all     - Build all binaries (API, Worker, Admin)"
+	@echo "  build-all     - Build all binaries (API, Worker)"
 	@echo "  clean         - Clean build artifacts"
 	@echo ""
 	@echo "Run:"
 	@echo "  run           - Run API server"
 	@echo "  run-worker    - Run background worker"
-	@echo "  run-admin     - Run admin panel"
 	@echo ""
 	@echo "Test & Lint:"
 	@echo "  test          - Run tests"
@@ -131,13 +127,16 @@ help:
 	@echo "  fmt           - Format code"
 	@echo "  vet           - Vet code"
 	@echo ""
-	@echo "Docker:"
-	@echo "  docker-build  - Build Docker images"
-	@echo "  docker-up     - Start Docker containers"
-	@echo "  docker-down   - Stop Docker containers"
-	@echo "  docker-logs   - View Docker logs"
-	@echo "  docker-dev    - Start in development mode"
-	@echo "  docker-restart- Restart all containers"
+	@echo "Docker (dev):"
+	@echo "  docker-build     - Build dev Docker images"
+	@echo "  docker-up        - Start dev containers (detached)"
+	@echo "  docker-down      - Stop dev containers"
+	@echo "  docker-logs      - View dev container logs"
+	@echo "  docker-dev       - Build and start dev containers (foreground)"
+	@echo "  docker-restart   - Restart dev containers"
+	@echo ""
+	@echo "Docker (prod):"
+	@echo "  docker-build-prod - Build production images (api, worker, admin)"
 	@echo ""
 	@echo "Database:"
 	@echo "  migrate-up    - Run database migrations"