Linux build needs libdbus for the keyring Secret Service backend

The sync Secret Service backend links system libdbus via libdbus-sys, so
the Linux CI job installs libdbus-1-dev + pkg-config and the PKGBUILD
declares dbus (build + runtime). Caught by the linux-cli CI job.

packaging/aur/PKGBUILD

@@ -11,8 +11,8 @@ pkgdesc="Local IMAP/SMTP bridge for Tuta encrypted email (headless CLI/daemon)"
 arch=('x86_64' 'aarch64')
 url="https://github.com/spartanz51/tutabridge"
 license=('GPL-3.0-or-later')
-depends=('gcc-libs')
-makedepends=('rust' 'cargo' 'git' 'cmake' 'nasm')
+depends=('gcc-libs' 'dbus')
+makedepends=('rust' 'cargo' 'git' 'cmake' 'nasm' 'dbus' 'pkgconf')
 optdepends=('gnome-keyring: persist the Tuta session across reboots (Secret Service)'
             'kwallet: alternative Secret Service provider')
 provides=('tutabridge')

packaging/aur/README.md

@@ -45,7 +45,10 @@ git commit -m "Initial import" && git push
 
 - `pkgver()` derives `0.r<commits>.<short-sha>` from git; `makepkg` rewrites the
   `pkgver=` line on each build.
-- Linux secret-service (keyring persistence) needs a running provider
+- The keyring Secret Service backend links system `libdbus` (via
+  `libdbus-sys`), so `dbus` is a build + runtime dependency. It's present on
+  essentially every Linux desktop already.
+- Keyring *persistence* additionally needs a running Secret Service provider
   (gnome-keyring / kwallet) — listed as optdepends. Without one the daemon
   still works but will ask for the Tuta password on every start.
 - A future tagged release can add a non-`-git` `tutabridge` package built from