feat: implement BDD testing with Godog

Implement comprehensive BDD testing framework using Godog:
- Added feature files for greet and health endpoints
- Created test server that runs on port 9191
- Implemented step definitions using Godog's exact patterns
- Fixed undefined step warnings by following Godog conventions
- All tests passing with proper response validation
- Maintained black box testing principles

Key files:
- pkg/bdd/steps/steps.go - Step definitions using StepContext struct
- pkg/bdd/testserver/ - Test server implementation
- features/*.feature - BDD feature files
- pkg/bdd/README.md - Documentation for proper step patterns

The implementation follows Godog's exact pattern suggestions to avoid
undefined step warnings and provides comprehensive API testing.

pkg/bdd/testserver/client.go

@@ -0,0 +1,54 @@
+package testserver
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+)
+
+type Client struct {
+	server   *Server
+	lastResp *http.Response
+	lastBody []byte
+}
+
+func NewClient(server *Server) *Client {
+	return &Client{
+		server: server,
+	}
+}
+
+func (c *Client) Request(method, path string, body []byte) error {
+	url := c.server.GetBaseURL() + path
+	req, err := http.NewRequest(method, url, nil)
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("request failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	c.lastResp = resp
+	c.lastBody, err = io.ReadAll(resp.Body)
+	if err != nil {
+		return fmt.Errorf("failed to read response body: %w", err)
+	}
+
+	return nil
+}
+
+func (c *Client) ExpectResponseBody(expected string) error {
+	if c.lastResp == nil {
+		return fmt.Errorf("no response received")
+	}
+
+	actual := string(c.lastBody)
+	if actual != expected {
+		return fmt.Errorf("expected response body %q, got %q", expected, actual)
+	}
+
+	return nil
+}