gui: native-backend session work + fix shim crashes; add page smoke test

Bundles the pending native-UI session (dark shell, style overhaul, audio
page) with review fixes:
- native Row: set_subtitle_lines + set_activatable_widget (store and
  online-accounts pages crashed with AttributeError under TANINUX_UI=native)
- wine page routed through the ui seam (last direct Adw import removed)
- console: delete no-op log_expander/collapsible_log and .clear() call sites
- ui/__init__ docstring now states the actual default backend (native)
- tests/test_pages_native.py builds every registered page under the native
  backend (29 pass; skips headless)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_pages_native.py

@@ -0,0 +1,71 @@
+"""Smoke test for the native (libadwaita-free) UI backend.
+
+Under ``TANINUX_UI=native`` every registered page must ``build()`` without
+tripping over a gap in the native widget shims (``ui/native.py``). The point is
+to catch ``AttributeError`` / ``TypeError`` — a missing method or a wrong kwarg
+on a shim — the kind of runtime crash that only surfaces when a page is opened.
+
+The test is deliberately tolerant of *environmental* failures: several pages
+call system tools (pacman, nmcli, gsettings, …) inside ``build()``. When such a
+call blows up we skip that page rather than fail — those are not shim gaps.
+
+Needs a display. If GTK cannot initialise (headless CI), the whole module is
+skipped at import time.
+"""
+from __future__ import annotations
+
+import os
+
+# Must be set before taninux.gui.ui is imported so the native backend is chosen.
+os.environ.setdefault("TANINUX_UI", "native")
+
+import pytest
+
+# --- GTK availability gate (module-level skip when there is no display) --------
+try:
+    import gi
+
+    gi.require_version("Gtk", "4.0")
+    from gi.repository import Gtk
+
+    _res = Gtk.init_check()
+    _gtk_ok = _res[0] if isinstance(_res, tuple) else bool(_res)
+except Exception as exc:  # noqa: BLE001 — any import/version error means no GTK
+    pytest.skip(f"GTK 4 unavailable: {exc}", allow_module_level=True)
+else:
+    if not _gtk_ok:
+        pytest.skip("GTK could not initialise (no display)", allow_module_level=True)
+
+from taninux.gui import ui  # noqa: E402
+from taninux.gui.pages import PAGES  # noqa: E402
+
+
+@pytest.fixture(scope="module")
+def window():
+    """An off-screen GTK root so built pages have a real window to parent into.
+
+    Deliberately never presented and never destroyed: realising/tearing down a
+    window here (while pages have spawned worker threads that post idle
+    callbacks) can crash GTK at interpreter shutdown. Leaving it for the OS to
+    reclaim keeps the smoke test stable.
+    """
+    ui.ensure_css()
+    win = Gtk.Window()
+    ui.set_dark(win, False)
+    yield win
+
+
+@pytest.mark.parametrize("page", PAGES, ids=lambda p: p.key)
+def test_page_builds(page, window):
+    try:
+        widget = page.build()
+    except (AttributeError, TypeError):
+        # A shim gap (missing method / wrong kwarg) — exactly what we hunt for.
+        raise
+    except Exception as exc:  # noqa: BLE001 — a system tool the sandbox lacks
+        pytest.skip(f"{page.key}: build() needs a live system resource: {exc!r}")
+
+    assert widget is not None, f"{page.key}.build() returned None"
+    # Parent it (unrealised) so the native container measure paths are exercised.
+    holder = Gtk.Box()
+    holder.append(widget)