gui: native libadwaita-free UI backend + dark shell; packaging/iso updates

- gui/ui: native GTK4 widget vocabulary (.tn-*) behind the ui.* seam,
  default backend now native; style_apple.css design language
- shell: sidebar/topbar/content all #0f0f0f in dark (matches eww panels)
- new pages: wine, online_accounts
- packaging: tanin-icons (accent folder theme), tanin-calendar, gtklock,
  taninux-gtk3-theme, flatpak install handler
- iso/distro: profile + manifest tweaks (ISO binary not included)

packaging/taninux-gtk3-theme/generate.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+"""Regeneriert die statischen CSS-Dateien aus gui/style.py.
+
+    cd packaging/taninux-gtk3-theme
+    PYTHONPATH=../../src python generate.py
+"""
+from pathlib import Path
+from taninux.gui.style import _gtk3_full
+from taninux.gui.accents import by_key
+
+acc = by_key("ume")
+here = Path(__file__).parent
+
+for dark, name in ((False, "TANINUX"), (True, "TANINUX-dark")):
+    dst = here / name / "gtk-3.0" / "gtk.css"
+    dst.parent.mkdir(parents=True, exist_ok=True)
+    dst.write_text(_gtk3_full(acc, dark))
+    print(f"  {dst.relative_to(here.parent.parent)}")