Add test library cleanup by name and documentation

Problem:
- Libraries are universal (not user-owned) and persist in database
- Tests create libraries via API but don't clean them up
- Libraries accumulate between test runs

Solution:
- Delete test libraries (names containing "test") during cleanup
- Uses case-insensitive matching to catch "Test", "TEST", "test", etc.
- Preserves user-created libraries without "test" in name

Changes:
1. cmd/server/tests/test_helpers.go:
   - Added library cleanup in setupTestServer() after user cleanup
   - Lists all libraries and deletes those with "test" in name
   - Includes warning comment about naming convention

2. docs/contributing/development.md:
   - Added "Test Library Naming Convention" section
   - Documents that "test" in library names triggers deletion
   - Recommends alternative names for persistent test libraries

Note: Users should NOT use "test" in library names if they want to keep them.

cmd/server/tests/test_helpers.go

@@ -529,6 +529,16 @@ func setupTestServer(t *testing.T) *TestServerSetup {
 		}
 	}
 
+	// Delete test libraries (names containing "test" - case insensitive)
+	// This cleans up libraries created by tests while preserving user-created libraries
+	// NOTE: Do not use "test" in library names if you want to keep them!
+	allLibs, _ := queries.ListLibraries(ctx)
+	for _, lib := range allLibs {
+		if strings.Contains(strings.ToLower(lib.Name), "test") {
+			queries.DeleteLibrary(ctx, lib.ID)
+		}
+	}
+
 	// Create fresh admin test user
 	passwordHash := "$2a$10$JjAtK7PPa1WexQC3AUGe8OXLeuseZ/haN1Mz7emMo6CfOvMiTVXWq"
 	adminUser, err := queries.CreateUser(ctx, database.CreateUserParams{

docs/contributing/development.md

@@ -279,6 +279,15 @@ Environment variables for testing:
 
 **⚠️ WARNING**: Never enable these in production!
 
+### Test Library Naming Convention
+
+Integration tests automatically clean up libraries with "test" in the name (case-insensitive).
+
+**⚠️ IMPORTANT**: Do not use "test" in library names if you want to keep them!
+- Libraries containing "test" (e.g., "My Test Library", "Test Library 1") will be deleted by test cleanup
+- Use names like "Development Library", "Staging Books", or "Personal" for libraries you want to keep
+- This ensures your manual test data persists between test runs
+
 ## 📝 Code Style Guidelines
 
 ### Go Code