Guard the v3 TUI test's textual import, as every other TUI test does

`textual` is not a declared dependency — not in dependencies, not an extra,
not in the dev group — so it is absent from any environment built from the
lockfile. Every other TUI test opens with pytest.importorskip("textual") and
skips. This file did not, so instead of skipping it failed COLLECTION, and a
collection error takes the whole run down: the entire Python suite went red
on Linux and macOS over a module no test here can rely on.

The guard is the immediate fix. The larger finding is recorded in TODO.md:
the whole TUI test surface has been passing by not running, and the step
meant to catch that — `seedpass tui2 --check` — uses find_spec and reports
"unavailable" with a zero exit, so it passes whether or not the TUI can
start. A fresh install from the lockfile ships a TUI that does not work and
nothing in CI says so. Which way to resolve that is a product call, so it is
written down rather than decided here.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01Vtx94nXDmNgXEeThUZP4QN

src/tests/test_tui_v3_parity.py

@@ -1,5 +1,13 @@
 from __future__ import annotations
 import pytest
+
+# textual is not a declared dependency, so it is absent from any environment
+# built from the lockfile. Every other TUI test guards its import this way;
+# this file did not, so instead of skipping it failed COLLECTION, which takes
+# the whole run down with it -- the entire Python suite went red on Linux and
+# macOS over a module no test here can rely on.
+pytest.importorskip("textual")
+
 from unittest.mock import MagicMock
 from rich.text import Text
 from textual.widgets import DataTable