iso: fix installer autostart (root uses zsh) + TANINUX branding

- /root/.zprofile launches tanin-installer on tty1 (root shell is zsh, so
  .bash_profile was ignored); striplive removes .zprofile on the target
- profiledef: MERGE releng's file_permissions (lost .automated_script.sh +x ->
  the 'permission denied' message) + keep our entries
- branding: TANINUX os-release/hostname/motd; bootstrap rebrands the boot menus

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

iso/overrides/airootfs/root/.bash_profile

@@ -1,6 +0,0 @@
-# Live ISO: on the first console (tty1), launch the TANINUX installer.
-# (On an installed system this file isn't present — Calamares' shellprocess
-#  strips the live-only bits from the target.)
-if [[ "$(tty)" == /dev/tty1 ]] && [[ -z "${WAYLAND_DISPLAY:-}" ]] && ! pgrep -x cage >/dev/null 2>&1; then
-  exec tanin-installer
-fi

iso/overrides/airootfs/root/.zprofile

@@ -0,0 +1,5 @@
+# Live ISO: auto-launch the TANINUX installer on the first console.
+# (Removed from the installed target by Calamares' shellprocess-striplive.)
+if [[ "$(tty)" == /dev/tty1 ]] && [[ -z "$WAYLAND_DISPLAY" ]] && ! pgrep -x cage >/dev/null 2>&1; then
+  exec tanin-installer
+fi