test: use real directories in TUI/integration project tests

ProjectService now rejects non-existent paths (path-validation feature), so
the TUI and integration tests must seed projects with real tmp_path dirs.
Completes the path-validation test updates beyond test_services.py.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_integration.py

@@ -43,11 +43,11 @@ def setup():
 
 
 @pytest.mark.asyncio
-async def test_full_lifecycle(setup):
+async def test_full_lifecycle(setup, tmp_path):
     proj_svc, sess_svc, tmux = setup
 
     # Create project
-    project = proj_svc.create(name="test-proj", path="/tmp/test-proj")
+    project = proj_svc.create(name="test-proj", path=str(tmp_path))
     assert project.id == 1
 
     # Create session