fix(tui): resolve format, AmbiguousStep, and coverage gaps in session persistence

- Apply ruff format to store.py (split multi-arg conn.execute calls) and
  steps file (collapse single-arg execute to one line)
- Fix AmbiguousStep: add literal quotes to @given/@then patterns so
  'a session with id "{session_id}"' is unambiguous vs the
  'in the database' variant; update all dependent then-steps consistently
- Mark if TYPE_CHECKING block with # pragma: no cover (never executed)
- Add scenario + step for default db_path to cover store.py lines 32-34
  (uses unittest.mock.patch on Path.home to avoid touching real homedir)

ISSUES CLOSED: #10648

features/tui_session_persistence.feature

@@ -45,3 +45,7 @@ Feature: TUI Session Persistence
     And I create a new session store instance
     Then the active session is "last-session"
     And the session data is restored correctly
+
+  Scenario: Store uses default database path when none is specified
+    Given the TUI session store is created with default database path
+    Then the SQLite database file exists at ~/.local/state/cleveragents/tui.db