refactor: clean up tests and templates for media-items system

- Remove ebook-specific test files (ebook_test.go, integration_test.go, notes_highlights_test.go)
- Update search_test.go for media-items API paths
- Regenerate templates (bookshelf_templ.go, header_templ.go)
- Add ISBN normalization utility function
- Clean up test suite to focus on media-items functionality

Aligns tests and templates with unified media-items architecture

cmd/server/tests/search_test.go

@@ -169,7 +169,7 @@ func TestSearchMediaItemsTests(t *testing.T) {
 	})
 
 	t.Run("Search with fuzzy match fallback", func(t *testing.T) {
-		req := httptest.NewRequest("GET", "/api/media-items/search?q=hary poter", nil)
+		req := httptest.NewRequest("GET", "/api/media-items/search?q=hary+poter", nil)
 		req.Header.Set("Authorization", "Bearer valid-token")
 		rr := httptest.NewRecorder()