feat: add build system and integration tests

- Update Makefile with test-coverage and verify targets
- Add build.sh script for cross-platform builds with SHA256 checksums
- Implement integration tests for full workflow (add/list/get/update/export/delete)
- Add config integration test
- Update project state documentation

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build run test clean lint fmt vet install release help
+.PHONY: build run test test-short test-coverage clean fmt vet lint install tidy deps verify release help
 
 # Binary name
 BINARY_NAME=hostkeeper
@@ -37,10 +37,17 @@ test:
 test-short:
 	$(GOTEST) ./... -v -short
 
+## test-coverage: Run tests with coverage report
+test-coverage:
+	$(GOTEST) ./... -v -coverprofile=coverage.out -covermode=atomic
+	$(GOCMD) tool cover -html=coverage.out -o coverage.html
+	@echo "Coverage report generated: coverage.html"
+
 ## clean: Remove build artifacts
 clean:
 	$(GOCLEAN)
 	rm -rf $(BUILD_DIR)
+	rm -f coverage.out coverage.html
 
 ## fmt: Format all Go files
 fmt:
@@ -66,6 +73,10 @@ tidy:
 deps:
 	$(GOCMD) mod download
 
+## verify: Verify module dependencies
+verify:
+	$(GOCMD) mod verify
+
 ## release: Build for multiple platforms
 release: clean
 	mkdir -p $(BUILD_DIR)