Add JWT base_url validation tests

Add 2 additional JWT authentication tests:
- test_init_with_empty_base_url_raises_error
- test_init_with_whitespace_base_url_raises_error

Improves JWT auth coverage slightly and adds validation coverage
for base_url parameter.

Tests: 442 → 444 (+2)
Coverage: 79.32% → 79.35% (+0.03%)

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

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

tests/auth/test_jwt.py

@@ -52,6 +52,16 @@ class TestJWTAuth:
         with pytest.raises(ValueError, match="JWT token cannot be empty"):
             JWTAuth(None, mock_wiki_base_url)
 
+    def test_init_with_empty_base_url_raises_error(self, mock_jwt_token):
+        """Test that empty base URL raises ValueError."""
+        with pytest.raises(ValueError, match="Base URL cannot be empty"):
+            JWTAuth(mock_jwt_token, "")
+
+    def test_init_with_whitespace_base_url_raises_error(self, mock_jwt_token):
+        """Test that whitespace-only base URL raises ValueError."""
+        with pytest.raises(ValueError, match="Base URL cannot be empty"):
+            JWTAuth(mock_jwt_token, "   ")
+
     def test_get_headers_returns_bearer_token(self, jwt_auth, mock_jwt_token):
         """Test that get_headers returns proper Authorization header."""
         headers = jwt_auth.get_headers()