Add devbox-shell bridge line to baked .bash_aliases

If the host bind-mounts ~/.config/devbox-shell/ into the container
(the directory-mount pattern that avoids single-file inode breakage),
the container needs a bridge line in .bashrc or .bash_aliases to
source the mounted file. Previously this bridge had to be re-added
manually after every --force-recreate because it lived in the
container's writable layer.

Baking it into the skel .bash_aliases makes it automatic: every
fresh container sources ~/.config/devbox-shell/bash_aliases if it
exists, with zero manual steps. Hosts that don't use the devbox-shell
pattern are unaffected — the [ -r ... ] test silently skips.

rootfs/home/developer/.bash_aliases

@@ -3,6 +3,15 @@
 # To override, bind-mount your host's ~/.bash_aliases over this file
 # via docker-compose.yml.
 
+# ── Host-shared shell customizations (devbox-shell bridge) ───────────
+# If the host bind-mounts a directory at ~/.config/devbox-shell/ (the
+# recommended pattern for sharing aliases/PATH/utilities between host
+# and container), source the bash_aliases file from it. This survives
+# --force-recreate because it's baked into the image's skel, not the
+# container's writable layer. Hosts that don't use this pattern are
+# unaffected — the test silently skips if the file doesn't exist.
+[ -r "$HOME/.config/devbox-shell/bash_aliases" ] && . "$HOME/.config/devbox-shell/bash_aliases"
+
 # ── History persistence and quality ──────────────────────────────────
 # The named volume devbox-shell-history is mounted at ~/.cache/bash
 # so history survives container recreation.