fix: validate_caldav_url crashes with TypeError on a non-string URL (#1608)

tests/test_caldav_url_nonstring.py

@@ -0,0 +1,22 @@
+"""Regression: validate_caldav_url must reject a non-string via its normal
+ValueError path, not crash with TypeError.
+
+It did `(raw_url or "").strip()`, so a non-string scalar (e.g. an int from a
+mis-typed config) reached `.strip()` and raised TypeError instead of the
+function\'s own ValueError.
+"""
+import pytest
+
+from src.caldav_sync import validate_caldav_url
+
+
+def test_non_string_raises_valueerror_not_typeerror():
+    with pytest.raises(ValueError):
+        validate_caldav_url(12345)
+    with pytest.raises(ValueError):
+        validate_caldav_url(None)
+
+
+def test_valid_url_passes():
+    out = validate_caldav_url("https://dav.example.com/calendars/")
+    assert "example.com" in out