fix: skip library.json test when bib.sqlite has no data (fixes CI)

The test assumed bib.sqlite always has items when present. In CI,
a stale or empty bib.sqlite could exist without data, causing the
export to produce an empty library.json. Now validates the database
has items before asserting on the export output.

tests/docs/test_docs_build.py

@@ -30,11 +30,20 @@ class TestExportLibrary:
         assert result.returncode == 0, result.stderr
 
     def test_library_json_has_items(self):
-        """library.json should have >0 items when bib.sqlite exists."""
+        """library.json should have >0 items when bib.sqlite has data."""
         if not BIB_DB.exists():
-            import pytest
-
             pytest.skip("bib.sqlite not available")
+        # Verify bib.sqlite is a real database with items
+        import sqlite3
+
+        try:
+            con = sqlite3.connect(str(BIB_DB))
+            count = con.execute("SELECT count(*) FROM items").fetchone()[0]
+            con.close()
+        except (sqlite3.OperationalError, sqlite3.DatabaseError):
+            pytest.skip("bib.sqlite is not a valid database")
+        if count == 0:
+            pytest.skip("bib.sqlite has no items")
         # Run the export
         subprocess.run([sys.executable, str(EXPORT_SCRIPT)], check=True)
         data = json.loads(LIBRARY_JSON.read_text())