Bench(fix[scripts]): Mark the runnable benchmark scripts executable

why: Each carries a `uv run --script` shebang and the docs invoke them
directly, but they shipped without the executable bit, so the shebang
described an invocation that could not work. ruff's EXE001 flags this on
Linux; the rule is skipped on Windows and WSL, so it only surfaces in CI.

what:
- Record bench_orchestration, orchestration_fuzzer, orchestration_matrix, and
  orchestration_stress as mode 755, matching the other runnable scripts

Author: tony