Add OpenAPI/Swagger documentation

- Add Swagger dependencies to go.mod
- Annotate all API endpoints with Swagger comments
- Add Swagger UI at /api/v1/docs endpoint
- Auto-generate Swagger docs in Dockerfile build
- Update README with API documentation link

internal/infrastructure/http/auth_handlers.go

@@ -44,6 +44,18 @@ type AuthResponse struct {
 	UserID string `json:"user_id"`
 }
 
+// Register godoc
+// @Summary Register a new user
+// @Description Create a new user account
+// @Tags auth
+// @Accept json
+// @Produce json
+// @Param request body RegisterRequest true "Registration data"
+// @Success 201 {object} AuthResponse
+// @Failure 400 {object} ErrorResponse
+// @Failure 409 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
+// @Router /auth/register [post]
 func (h *AuthHandlers) Register(w http.ResponseWriter, r *http.Request) {
 	var req RegisterRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
@@ -83,6 +95,18 @@ func (h *AuthHandlers) Register(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
+// Login godoc
+// @Summary Login user
+// @Description Authenticate user and get JWT token
+// @Tags auth
+// @Accept json
+// @Produce json
+// @Param request body LoginRequest true "Login credentials"
+// @Success 200 {object} AuthResponse
+// @Failure 400 {object} ErrorResponse
+// @Failure 401 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
+// @Router /auth/login [post]
 func (h *AuthHandlers) Login(w http.ResponseWriter, r *http.Request) {
 	var req LoginRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {