fix: add runtime schema guard for skipped count

tests/test_db_schema.py

@@ -0,0 +1,27 @@
+from sqlalchemy import create_engine, inspect, text
+
+from app.db import _ensure_runtime_schema
+
+
+def test_runtime_schema_adds_skipped_count_to_existing_crawl_runs_table(monkeypatch):
+    engine = create_engine("sqlite:///:memory:")
+    with engine.begin() as connection:
+        connection.execute(
+            text(
+                """
+                CREATE TABLE crawl_runs (
+                  id INTEGER PRIMARY KEY,
+                  source_url TEXT NOT NULL,
+                  status VARCHAR(32) NOT NULL DEFAULT 'running',
+                  found_count INTEGER NOT NULL DEFAULT 0,
+                  parsed_count INTEGER NOT NULL DEFAULT 0
+                )
+                """
+            )
+        )
+    monkeypatch.setattr("app.db.engine", engine)
+
+    _ensure_runtime_schema()
+
+    columns = {column["name"] for column in inspect(engine).get_columns("crawl_runs")}
+    assert "skipped_count" in columns