fix(dashboard): proot-safe copy (cp -a) instead of rsync -Aax

[luisguzman-adfa]

rsync sets perms without following symlinks via lchmod = fchmodat(AT_SYMLINK_NOFOLLOW); glibc >=2.39 (Debian trixie 2.41) services that with the fchmodat2() syscall (Linux

=6.6). proot does not translate fchmodat2's path arg, so under proot on a 6.6+ kernel
the guest path reaches the host untranslated and chmod returns ENOENT -> rsync exits 23 -> install_iiaboa_dashboard aborts (set -e) -> rootfs lacks flag_install_ready and the dashboard never starts. Reproduced building the rootfs off-device on a Raspberry Pi 5 (kernel 6.8) for BOTH armeabi-v7a and arm64-v8a; it worked on kernel 6.1 hosts and in the APK -> host-kernel-dependent, not arch-specific. cp uses plain chmod (old fchmodat), which proot translates, so the copy is reliable.

Device-to-device sync is unaffected: its rsync is the static librsync.so built with lchmod disabled (ac_cv_func_lchmod=no), so it never calls fchmodat2.

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