ISO: microcode + plymouth hooks, PDF/VA-API packages, first-run network

- post-install: ensure the `microcode` initramfs hook (after autodetect) so
  installed systems carry CPU ucode — the live ISO embeds it, so nothing is
  staged onto the target otherwise. Rebuild all presets with `mkinitcpio -P`.
- post-install: drop the nonexistent `sd-plymouth` hook branch; only the udev
  `plymouth` hook exists. Set the theme then rebuild once.
- packages: add zathura + zathura-pdf-mupdf (BOS had no PDF viewer) and
  libva-utils (`vainfo`); the Mesa VA-API backend now ships in `mesa` itself.
- bos-welcome: on first run, if NetworkManager isn't fully online, open nmtui
  so the user connects before the first bos-update/pacman (avoids confusing DNS
  errors on a fresh install). Float the bos-netsetup window like bos-welcome.

iso/packages.x86_64

@@ -139,10 +139,13 @@ file-roller
 
 # GUI applications a general desktop is expected to have out of the box.
 # gnome-text-editor: graphical editor (terminal editors aside); gnome-calculator:
-# calculator; loupe: Wayland-native image viewer (default for image files).
+# calculator; loupe: Wayland-native image viewer (default for image files);
+# zathura(+pdf-mupdf): lightweight Wayland PDF viewer (BOS had no PDF reader).
 gnome-text-editor
 gnome-calculator
 loupe
+zathura
+zathura-pdf-mupdf
 # Media player — BOS ships gstreamer codecs but otherwise has no player app.
 vlc
 # Web browser (served from the [Breadway] repo; AUR zen-browser-bin republished
@@ -190,6 +193,12 @@ plymouth
 gst-plugins-good
 gst-plugins-bad
 gst-plugins-ugly
+# Hardware video acceleration (VA-API) — lets the AMD/Intel GPU decode H.264/HEVC/
+# VP9 in mpv, VLC, and browsers instead of the CPU (cooler, longer battery on
+# video). The open Mesa VA-API backend (radeonsi_drv_video.so etc.) now ships in
+# the `mesa` package itself (pulled in already), so only libva (deps) + the
+# `vainfo` verification tool need listing here.
+libva-utils
 # GUI audio mixer — useful when output device needs manual switching.
 pavucontrol