feat: add URL validator for X Space URLs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/test_validator.py

@@ -0,0 +1,12 @@
+import pytest
+from src.validator import validate_space_url
+
+
+def test_validate_space_url_valid():
+    """Test that valid X Space URL is accepted."""
+    url = "https://x.com/i/spaces/1ZkKzZWnVRRKv"
+    is_valid, space_id, error = validate_space_url(url)
+
+    assert is_valid is True
+    assert space_id == "1ZkKzZWnVRRKv"
+    assert error is None