test: address PR review — shared fixtures, coverage, hygiene

Extract Flask client fixtures to tests/conftest.py, use client_single
for search limit tests, and relax session count assertion to >= 1.
Include utils/ in coverage (omit untested export modules), stop
tracking .coverage, and align integration-tests CI with full cov scope.

Co-Authored-By: Cursor <cursoragent@cursor.com>

Author: clean6378-max-it

tests/conftest.py

@@ -39,7 +39,7 @@ def client(tmp_path):
 
 @pytest.fixture
 def client_single(tmp_path):
-    """Flask test client with one seeded session — for search/limit tests."""
+    """Flask test client with one seeded session ? for search/limit tests."""
     return _make_test_client(tmp_path, {"session_abc123.jsonl": "session_minimal.jsonl"})