Fix CI build and update Makefile to build all services

- Add $HOME/go/bin to PATH using $GITHUB_PATH for protoc plugins
- Update Makefile build target to build all service binaries:
  - platform, api-gateway, auth-service, identity-service, authz-service, audit-service
- Update CI workflow to use 'make build' instead of individual commands
- Upload all service binaries as CI artifacts
- Fixes protoc plugin discovery and ensures all services are built

Makefile

@@ -18,7 +18,7 @@ help:
 	@echo "  make lint          - Run linters"
 	@echo "  make fmt           - Format code"
 	@echo "  make fmt-check     - Check code formatting"
-	@echo "  make build         - Build platform and api-gateway binaries"
+	@echo "  make build         - Build all service binaries"
 	@echo "  make clean         - Clean build artifacts"
 	@echo "  make docker-build  - Build Docker image"
 	@echo "  make docker-run    - Run Docker container"
@@ -85,10 +85,14 @@ fmt-check:
 	@echo "Code is properly formatted"
 
 build:
-	@echo "Building platform and api-gateway binaries..."
+	@echo "Building all service binaries..."
 	$(GO) build -v -o bin/platform ./cmd/platform
 	$(GO) build -v -o bin/api-gateway ./cmd/api-gateway
-	@echo "Build complete: bin/platform, bin/api-gateway"
+	$(GO) build -v -o bin/auth-service ./cmd/auth-service
+	$(GO) build -v -o bin/identity-service ./cmd/identity-service
+	$(GO) build -v -o bin/authz-service ./cmd/authz-service
+	$(GO) build -v -o bin/audit-service ./cmd/audit-service
+	@echo "Build complete: bin/platform, bin/api-gateway, bin/auth-service, bin/identity-service, bin/authz-service, bin/audit-service"
 
 clean:
 	@echo "Cleaning build artifacts..."