Refactor to JSON API with Chi router and interface-based design

- Add pkg/greet/api_v1.go with ApiV1Greet interface and handler
- Implement Greeter interface for dependency injection
- Return JSON responses with proper Content-Type headers
- Move greet service instantiation to server package
- Separate v1 route registration into registerApiV1Routes function
- Health endpoint at /api level, greet endpoints at /api/v1/greet
- Simplify server entrypoint by removing external dependencies

pkg/greet/api_v1.go

@@ -0,0 +1,44 @@
+package greet
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+)
+
+type Greeter interface {
+	Greet(name string) string
+}
+
+type ApiV1Greet interface {
+	RegisterRoutes(router chi.Router)
+}
+
+type apiV1GreetHandler struct {
+	greeter Greeter
+}
+
+func NewApiV1GreetHandler(greeter Greeter) ApiV1Greet {
+	return &apiV1GreetHandler{greeter: greeter}
+}
+
+func (h *apiV1GreetHandler) RegisterRoutes(router chi.Router) {
+	router.Get("/", h.handleGreetQuery)
+	router.Get("/{name}", h.handleGreetPath)
+}
+
+func (h *apiV1GreetHandler) handleGreetQuery(w http.ResponseWriter, r *http.Request) {
+	name := r.URL.Query().Get("name")
+	h.writeJSONResponse(w, h.greeter.Greet(name))
+}
+
+func (h *apiV1GreetHandler) handleGreetPath(w http.ResponseWriter, r *http.Request) {
+	name := chi.URLParam(r, "name")
+	h.writeJSONResponse(w, h.greeter.Greet(name))
+}
+
+func (h *apiV1GreetHandler) writeJSONResponse(w http.ResponseWriter, message string) {
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(map[string]string{"message": message})
+}