GTK theme: persistent dconf override for prefer-dark + adw-gtk3-dark

Operator 2026-05-10: "window opens and works (not the mios.toml
defined prefer-dark mode yet)" -- GUI apps render correctly via
the cairo software path but were falling back to upstream light
Adwaita instead of MiOS's intended dark theme.

Root cause: live `gsettings set` writes only land in the user-db
(per-user ~/.config/dconf/user) and don't survive wsl --shutdown.
Without a system-db cascade, every fresh user-bus session reverts
to upstream defaults.

Fix: ship a dconf system-db override at
/etc/dconf/db/local.d/00-mios-theme + /etc/dconf/profile/user.
Compiled into the binary system-db by `dconf update` (wired into
build-mios.ps1's overlay phase right after the seed step). The
local system-db then cascades into every user dconf profile at
login, so operators see adw-gtk3-dark + prefer-dark + Adwaita
icons + Adwaita Sans 11 + GeistMono Nerd Font Mono 10 + standard
GNOME window button layout on first GTK app launch.

Operator-overridable per-user (gsettings set ... or GNOME Tweaks)
without touching the system file.

.gitignore allowlist entries added for /etc/dconf/db/local.d/* +
/etc/dconf/profile/* so the override files are tracked.

Author: Kabuki94

.gitignore

@@ -161,6 +161,16 @@ etc/fapolicyd/*
 !/etc/systemd/user/**/
 !/etc/systemd/user/**/10-mios-*.conf
 
+# /etc/dconf/ -- system-wide GNOME / GTK defaults (color scheme,
+# gtk-theme, icon-theme, fonts). Cascade applied to every user-bus
+# at login; operator overrides per-user via gsettings / Tweaks.
+!/etc/dconf/
+!/etc/dconf/db/
+!/etc/dconf/db/local.d/
+!/etc/dconf/db/local.d/*
+!/etc/dconf/profile/
+!/etc/dconf/profile/*
+
 # /etc/mios/ -- KB config (system-prompts, kb.conf.toml, eval-criteria.json) tracked here.
 # Runtime secrets and per-host overrides are NOT tracked (handled by mios-bootstrap.git).
 !/etc/mios/

etc/dconf/db/local.d/00-mios-theme

@@ -0,0 +1,26 @@
+# /etc/dconf/db/local.d/00-mios-theme
+#
+# MiOS canonical GNOME / GTK theming defaults. Applied at every
+# user-bus login via dconf's system-db cascade -- operator sees
+# adw-gtk3-dark + prefer-dark color scheme on first launch of any
+# GTK app without having to gsettings-set it themselves.
+#
+# Operator-overridable per-user (gsettings set ... or the GNOME
+# Tweaks UI). System defaults here only take effect when the
+# user-db doesn't have a key set.
+#
+# /etc/dconf/profile/user (ships alongside this file) wires the
+# local system-db into the user dconf profile cascade.
+
+[org/gnome/desktop/interface]
+color-scheme='prefer-dark'
+gtk-theme='adw-gtk3-dark'
+icon-theme='Adwaita'
+cursor-theme='Adwaita'
+font-name='Adwaita Sans 11'
+monospace-font-name='GeistMono Nerd Font Mono 10'
+document-font-name='Adwaita Sans 11'
+
+[org/gnome/desktop/wm/preferences]
+theme='adw-gtk3-dark'
+button-layout='appmenu:minimize,maximize,close'

etc/dconf/profile/user

@@ -0,0 +1,2 @@
+user-db:user
+system-db:local