Add check-go guard with friendly message for missing Go toolchain

Makefile

@@ -20,32 +20,60 @@ GOVET := $(GOCMD) vet
 # Cross-compilation targets
 TARGETS := linux-amd64 linux-arm64 darwin-arm64 windows-amd64 windows-arm64
 
-# Platform detection
+# Platform detection (noiseless fallback — true check happens in check-go target)
-GOOS := $(shell go env GOOS)
+GOOS := $(shell go env GOOS 2>/dev/null || echo "unknown")
-GOARCH := $(shell go env GOARCH)
+GOARCH := $(shell go env GOARCH 2>/dev/null || echo "unknown")
+
+# ──────────────────────────────────────────────
+# Friendly Go-not-found guard
+check-go:
+	@if ! command -v go >/dev/null 2>&1; then \
+		echo ""; \
+		echo "  ╭──────────────────────────────────────────────╮"; \
+		echo "  │  ⚠  Go is not installed on this machine     │"; \
+		echo "  ├──────────────────────────────────────────────┤"; \
+		echo "  │                                              │"; \
+		echo "  │  obm is a Go project. You need the Go        │"; \
+		echo "  │  toolchain to build from source.             │"; \
+		echo "  │                                              │"; \
+		echo "  │  Install Go:                                 │"; \
+		echo "  │    Linux:  your package manager              │"; \
+		echo "  │            or https://go.dev/dl/             │"; \
+		echo "  │                                              │"; \
+		echo "  │    macOS:  brew install go                   │"; \
+		echo "  │                                              │"; \
+		echo "  │    Windows: https://go.dev/dl/               │"; \
+		echo "  │                                              │"; \
+		echo "  │  Or use the all-in-one script:               │"; \
+		echo "  │    ./scripts/install.sh                      │"; \
+		echo "  │                                              │"; \
+		echo "  ╰──────────────────────────────────────────────╯"; \
+		echo ""; \
+		exit 1; \
+	fi
 
 all: lint test build
 
-build:
+build: check-go
 	@echo "Building $(BINARY) v$(VERSION) for $(GOOS)/$(GOARCH)..."
 	$(GOBUILD) $(LDFLAGS) -o $(BINARY) ./cmd/obm
 
-test:
+test: check-go
 	@echo "Running tests..."
 	$(GOTEST) -v -race -coverprofile=coverage.out ./...
 
 lint: vet fmt
 	@echo "✓ Lint pass"
 
-vet:
+vet: check-go
 	@echo "Running go vet..."
 	$(GOVET) ./...
 
-fmt:
+fmt: check-go
 	@echo "Formatting code..."
 	gofmt -l -s -w .
 
-clean:
+clean: check-go
 	@echo "Cleaning..."
 	rm -f $(BINARY)
 	rm -f coverage.out
@@ -67,7 +95,7 @@ version:
 	@echo "$(VERSION)"
 
 # Cross-compilation
-cross-compile:
+cross-compile: check-go
 	@echo "Cross-compiling for all platforms..."
 	@mkdir -p bin
 	@for target in $(TARGETS); do \
@@ -84,23 +112,23 @@ cross-compile:
 	@echo "✓ Cross-compilation complete"
 
 # Build specific platform
-build-linux-amd64:
+build-linux-amd64: check-go
 	@mkdir -p bin
 	GOOS=linux GOARCH=amd64 CGO_ENABLED=0 $(GOBUILD) $(LDFLAGS) -o bin/linux-amd64/$(BINARY) ./cmd/obm
 
-build-linux-arm64:
+build-linux-arm64: check-go
 	@mkdir -p bin
 	GOOS=linux GOARCH=arm64 CGO_ENABLED=0 $(GOBUILD) $(LDFLAGS) -o bin/linux-arm64/$(BINARY) ./cmd/obm
 
-build-darwin-arm64:
+build-darwin-arm64: check-go
 	@mkdir -p bin
 	GOOS=darwin GOARCH=arm64 CGO_ENABLED=0 $(GOBUILD) $(LDFLAGS) -o bin/darwin-arm64/$(BINARY) ./cmd/obm
 
-build-windows-amd64:
+build-windows-amd64: check-go
 	@mkdir -p bin
 	GOOS=windows GOARCH=amd64 CGO_ENABLED=0 $(GOBUILD) $(LDFLAGS) -o bin/windows-amd64/$(BINARY).exe ./cmd/obm
 
-build-windows-arm64:
+build-windows-arm64: check-go
 	@mkdir -p bin
 	GOOS=windows GOARCH=arm64 CGO_ENABLED=0 $(GOBUILD) $(LDFLAGS) -o bin/windows-arm64/$(BINARY).exe ./cmd/obm
 
@@ -140,10 +168,10 @@ dev: build test
 	@echo "✓ Development build complete"
 
 # Quick test during development
-quick-test:
+quick-test: check-go
 	$(GOTEST) -race ./...
 
 # Coverage report
-coverage: test
+coverage: check-go test
 	$(GOCMD) tool cover -html=coverage.out -o coverage.html
 	@echo "Coverage report: coverage.html"