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/tanin-calendar/install-local.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Install tanin-calendar on THIS machine (no packaging round-trip). Run with
+# sudo:
+#   sudo bash packaging/tanin-calendar/install-local.sh
+set -euo pipefail
+SRC="$(cd "$(dirname "$0")" && pwd)"
+
+install -Dm755 "$SRC/tanin-calendar" /usr/bin/tanin-calendar
+install -Dm644 "$SRC/tanin-calendar.css" /usr/share/tanin/calendar/tanin-calendar.css
+install -Dm644 "$SRC/ch.gabrielevarano.TaninCalendar.desktop" \
+  /usr/share/applications/ch.gabrielevarano.TaninCalendar.desktop
+
+# refresh the desktop database so the launcher entry shows up immediately
+command -v update-desktop-database >/dev/null 2>&1 && \
+  update-desktop-database /usr/share/applications || true
+
+cat <<EOF
+tanin-calendar installed.
+  binary:  /usr/bin/tanin-calendar
+  css:     /usr/share/tanin/calendar/tanin-calendar.css
+  desktop: /usr/share/applications/ch.gabrielevarano.TaninCalendar.desktop
+
+Needs evolution-data-server (typelibs) + at least one calendar added in
+GNOME Online Accounts (or a local EDS calendar). Launch:  tanin-calendar
+EOF