refactor(tests): enhance test infrastructure with library/collection helpers

- Add LibraryTestData struct to TestDeviceSetup
- Implement CreateLibrary() for proper library creation in tests
- Implement CreateCollection() for test collection support
- Improve test isolation with dedicated library creation

This provides a more robust foundation for integration tests that need
proper library management support.

cmd/server/tests/user_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bookhoard/internal/handlers"
 	"bytes"
 	"encoding/json"
 	"net/http"
@@ -40,11 +41,11 @@ func TestUserProfileEndpoints(t *testing.T) {
 		rr := httptest.NewRecorder()
 
 		handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			profile := map[string]interface{}{
-				"id":       userID.String(),
-				"email":    "user@example.com",
-				"username": "testuser",
-				"role":     "user",
+			profile := handlers.UserProfile{
+				ID:       userID.String(),
+				Email:    "user@example.com",
+				Username: "testuser",
+				Role:     "user",
 			}
 			w.WriteHeader(http.StatusOK)
 			json.NewEncoder(w).Encode(profile)
@@ -79,8 +80,8 @@ func TestUserProfileEndpoints(t *testing.T) {
 // TestUserUpdateEndpoints tests user field update endpoints
 func TestUserUpdateEndpoints(t *testing.T) {
 	t.Run("PUT /api/auth/email - Update email to existing email", func(t *testing.T) {
-		payload := map[string]interface{}{
-			"email": "existing@example.com",
+		payload := handlers.UpdateEmailRequest{
+			Email: "existing@example.com",
 		}
 		jsonData, _ := json.Marshal(payload)
 
@@ -90,15 +91,14 @@ func TestUserUpdateEndpoints(t *testing.T) {
 		rr := httptest.NewRecorder()
 
 		handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			var req map[string]interface{}
+			var req handlers.UpdateEmailRequest
 			if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 				w.WriteHeader(http.StatusBadRequest)
 				w.Write([]byte(`{"error":"invalid request"}`))
 				return
 			}
 
-			email := req["email"].(string)
-			if email == "existing@example.com" {
+			if req.Email == "existing@example.com" {
 				w.WriteHeader(http.StatusConflict)
 				w.Write([]byte(`{"error":"email already taken"}`))
 				return
@@ -112,8 +112,8 @@ func TestUserUpdateEndpoints(t *testing.T) {
 	})
 
 	t.Run("PUT /api/auth/email - Update email with invalid format", func(t *testing.T) {
-		payload := map[string]interface{}{
-			"email": "invalid-email",
+		payload := handlers.UpdateEmailRequest{
+			Email: "invalid-email",
 		}
 		jsonData, _ := json.Marshal(payload)
 
@@ -123,14 +123,14 @@ func TestUserUpdateEndpoints(t *testing.T) {
 		rr := httptest.NewRecorder()
 
 		handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			var req map[string]interface{}
+			var req handlers.UpdateEmailRequest
 			if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 				w.WriteHeader(http.StatusBadRequest)
 				w.Write([]byte(`{"error":"invalid request"}`))
 				return
 			}
 
-			email, _ := req["email"].(string)
+			email := req.Email
 			if !contains(email, "@") || !contains(email, ".") {
 				w.WriteHeader(http.StatusBadRequest)
 				w.Write([]byte(`{"error":"email is invalid"}`))
@@ -145,8 +145,8 @@ func TestUserUpdateEndpoints(t *testing.T) {
 	})
 
 	t.Run("PUT /api/auth/email - Update email with empty value", func(t *testing.T) {
-		payload := map[string]interface{}{
-			"email": "",
+		payload := handlers.UpdateEmailRequest{
+			Email: "",
 		}
 		jsonData, _ := json.Marshal(payload)
 
@@ -165,8 +165,8 @@ func TestUserUpdateEndpoints(t *testing.T) {
 	})
 
 	t.Run("PUT /api/auth/username - Update username to existing username", func(t *testing.T) {
-		payload := map[string]interface{}{
-			"username": "existinguser",
+		payload := handlers.UpdateUsernameRequest{
+			Username: "existinguser",
 		}
 		jsonData, _ := json.Marshal(payload)
 
@@ -176,15 +176,14 @@ func TestUserUpdateEndpoints(t *testing.T) {
 		rr := httptest.NewRecorder()
 
 		handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			var req map[string]interface{}
+			var req handlers.UpdateUsernameRequest
 			if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 				w.WriteHeader(http.StatusBadRequest)
 				w.Write([]byte(`{"error":"invalid request"}`))
 				return
 			}
 
-			username := req["username"].(string)
-			if username == "existinguser" {
+			if req.Username == "existinguser" {
 				w.WriteHeader(http.StatusConflict)
 				w.Write([]byte(`{"error":"username already taken"}`))
 				return