refactor(tests): update test helpers and all test file references

- Rename createTestEbookID to createTestMediaItemID in test_helpers.go
- Update test helper comments and variable names (ebookReq -> mediaItemReq, etc.)
- Update all test file references:
  - analytics_test.go
  - book_matching_test.go
  - collections_bulk_test.go
  - kobo_test.go
  - media_bulk_test.go
  - opds_test.go
- Rename ebookID variable to mediaItemID in kobo_test.go
- Update test data to use 'Test Media Item' instead of 'Test Ebook'

cmd/server/tests/kobo_test.go

@@ -22,7 +22,7 @@ func TestKoboInitialization(t *testing.T) {
 
 	token := loginTestUser(t, ts, db)
 	_ = getTestUserID(t, db)
-	_ = createTestEbookID(t, ts, token)
+	_ = createTestMediaItemID(t, ts, token)
 
 	t.Run("successful initialization", func(t *testing.T) {
 		req, _ := http.NewRequest("GET", ts.URL+"/api/sync/kobo/test-token/v1/initialization", nil)
@@ -46,7 +46,7 @@ func TestKoboLibrarySync(t *testing.T) {
 	defer closeTestServer(t, ts, db)
 
 	token := loginTestUser(t, ts, db)
-	_ = createTestEbookID(t, ts, token)
+	_ = createTestMediaItemID(t, ts, token)
 
 	t.Run("successful library sync", func(t *testing.T) {
 		req, _ := http.NewRequest("GET", ts.URL+"/api/sync/kobo/test-token/v1/initialization", nil)
@@ -70,13 +70,13 @@ func TestKoboMarkupSync(t *testing.T) {
 	defer closeTestServer(t, ts, db)
 
 	token := loginTestUser(t, ts, db)
-	ebookID := createTestEbookID(t, ts, token)
+	mediaItemID := createTestMediaItemID(t, ts, token)
 
 	t.Run("successful markup sync with annotations and bookmarks", func(t *testing.T) {
 		reqBody := map[string]interface{}{
 			"ReadingSync": []map[string]interface{}{
 				{
-					"ContentId":            ebookID,
+					"ContentId":            mediaItemID,
 					"PercentRead":          45.6,
 					"EntitlementId":        "ent-123",
 					"RemainingTimeMinutes": 120,
@@ -86,14 +86,14 @@ func TestKoboMarkupSync(t *testing.T) {
 			"BookmarkSync": []map[string]interface{}{
 				{
 					"BookmarkId":    "bookmark-1",
-					"ContentId":     ebookID,
+					"ContentId":     mediaItemID,
 					"BookmarkText":  "This is highlighted text",
 					"BookmarkType":  "annotation",
 					"BookmarkTitle": "Chapter 3",
 				},
 				{
 					"BookmarkId":   "bookmark-2",
-					"ContentId":    ebookID,
+					"ContentId":    mediaItemID,
 					"BookmarkText": "This is my note abouts book",
 					"BookmarkType": "bookmark",
 				},
@@ -126,14 +126,14 @@ func TestKoboBookmarkSync(t *testing.T) {
 	defer closeTestServer(t, ts, db)
 
 	token := loginTestUser(t, ts, db)
-	ebookID := createTestEbookID(t, ts, token)
+	mediaItemID := createTestMediaItemID(t, ts, token)
 
 	t.Run("successful bookmark sync", func(t *testing.T) {
 		reqBody := map[string]interface{}{
 			"BookmarkSync": []map[string]interface{}{
 				{
 					"BookmarkId":   "bookmark-3",
-					"ContentId":    ebookID,
+					"ContentId":    mediaItemID,
 					"BookmarkText": "Important note abouts book",
 					"BookmarkType": "bookmark",
 					"DateCreated":  "2026-01-30T19:55:00Z",
@@ -167,14 +167,14 @@ func TestKoboAnalyticsGettests(t *testing.T) {
 	defer closeTestServer(t, ts, db)
 
 	token := loginTestUser(t, ts, db)
-	ebookID := createTestEbookID(t, ts, token)
+	mediaItemID := createTestMediaItemID(t, ts, token)
 
 	t.Run("successful analytics tests", func(t *testing.T) {
 		reqBody := map[string]interface{}{
 			"meta": map[string]string{
 				"name": "Kobo Analytics Tests",
 			},
-			"ContentId":        ebookID,
+			"ContentId":        mediaItemID,
 			"ReadingEvent":     "Reading",
 			"RemainingTimeMin": 180,
 			"PercentRead":      67.8,