fix: complete the deploy-tool dependency gate (end the whack-a-mole)

deploy-disk.sh had its own hardcoded tool check that was out of sync with
check-host-deps.sh, so builds got past the host gate and then failed at
deploy time with "missing host tool mkfs.btrfs" (btrfs-progs was never in
check-host-deps.sh).

- check-host-deps.sh: add mkfs.btrfs/btrfs (btrfs-progs) plus curl/git so
  `make deps` / check-host-deps --install covers the entire build + deploy
  path in one go.
- deploy-disk.sh: pre-flight now checks the full tool set (sgdisk,
  partprobe, mkfs.btrfs, btrfs, rsync, wipefs, truncate, + mkfs.vfat for
  efi) and reports ALL missing tools at once with the exact apt install
  command, instead of dying on the first one.
- build-live.sh: the live image explicitly installs gdisk, parted,
  dosfstools, btrfs-progs, rsync so the graphical installer always has the
  deploy tooling regardless of edition.

scripts/build-live.sh

@@ -55,12 +55,15 @@ chroot_run() { chroot "$LIVE_ROOT" /bin/bash -c "$*"; }
 # ── 2. install live session packages ────────────────────────────────────────
 log "[1/4] installing live-boot + X + installer dependencies"
 mount_pseudo
+# deploy tooling (gdisk parted dosfstools btrfs-progs rsync) is needed by
+# deploy-disk.sh, which the graphical installer runs against the target disk.
 chroot_run "export DEBIAN_FRONTEND=noninteractive
 apt-get update -qq
 apt-get install -y --no-install-recommends \
   live-boot live-config-systemd live-tools \
   xserver-xorg x11-xserver-utils openbox \
-  python3-gi gir1.2-gtk-3.0 gdisk parted dosfstools \
+  python3-gi gir1.2-gtk-3.0 \
+  gdisk parted dosfstools btrfs-progs rsync \
   | tee /tmp/live-packages.log"
 
 # Modern Xorg refuses to run as root, so the live session runs as a dedicated