fix(macos): omit AppleDouble members from preset and support-bundle archives

[roshangupta00750]

Fixes #7341

This combines #6160 (preset import) and #6159 (support bundle), both closed with the public-beta retirement (#7253) and rebased here onto main. Both are the same macOS defect in different archive writers.

Problem

macOS tar (bsdtar) adds an AppleDouble ._<name> member for every file with extended attributes, and hides those members from its own tar -tzf listing.

• ods preset export / ods preset import:
  • A preset exported on macOS leads with ._<name>.
  • preset import takes the first member as the preset name, so on Linux it resolves to ._<name> and fails with Invalid preset: missing meta.txt.
  • The real preset has already been extracted by then, so a retry asks to overwrite it.
• scripts/ods-support-bundle.sh: the diagnostics bundle carries binary ._* companions next to the real files.

Change

• Run both archive writers under COPYFILE_DISABLE=1, as ods-backup.sh already does (fix(backup): omit macOS AppleDouble metadata so compressed backups restore #5765). GNU tar ignores the variable.
• preset import skips ._* entries when it takes the preset name, so archives exported from macOS before this fix still import.

Tests

• tests/test-preset-macos-appledouble.sh (new, registered in tests/ci-suite.txt):
  • builds, with Python tarfile, an archive that leads with a ._<name> member the way bsdtar writes it, and imports it with the real CLI;
  • asserts the export guard;
  • on macOS, also exports a real preset and checks its raw members.
• tests/test-support-bundle.sh (already run by test-linux.yml):
  • checks the raw archive members with tarfile, because bsdtar's own listing hides ._*;
  • asserts the COPYFILE_DISABLE guard, which keeps the check deterministic on Linux.

	macOS (/bin/bash 3.2)	Linux, Ubuntu 26.04
preset test on main	4 passed, 2 failed	4 passed, 2 failed
preset test, this PR	6/6	6/6
support-bundle test on main	3 failed: ._* members really present in the bundle, plus the guard check	1 failed (guard check)
support-bundle test, this PR	1 failed	22/22

The one macOS support-bundle failure left with this PR (support bundle did not use selected Bash for nested project scripts) also fails on main and is unrelated.

list-unwired-tests.py --check passes, shellcheck -S warning is clean, and bash -n passes.

AI assistance was used for analysis and drafting the fix and tests. I reproduced both problems on macOS and verified the base-fail and fix-pass results above on macOS and Linux myself.