fix: allow empty CRAWL_LIMIT env value

tests/test_api_mcp.py

@@ -18,7 +18,7 @@ def test_health_returns_versions():
     response = client.get("/api/health")
 
     assert response.status_code == 200
-    assert response.json()["backend_version"] == "0.2.6"
+    assert response.json()["backend_version"] == "0.2.7"
 
 
 def test_mcp_requires_token_and_lists_tools():

tests/test_config.py

@@ -0,0 +1,13 @@
+from app.config import Settings
+
+
+def test_empty_crawl_limit_is_treated_as_none():
+    settings = Settings(crawl_limit="")
+
+    assert settings.crawl_limit is None
+
+
+def test_numeric_crawl_limit_is_parsed():
+    settings = Settings(crawl_limit="25")
+
+    assert settings.crawl_limit == 25