feat: add OS compatibility checks before running platform-specific logic

- lib/common.sh: add require_local_os, require_remote_os, require_remote_pkg_manager
- setup/macbook.sh: require macOS (Darwin)
- setup/unraid.sh: require remote is Linux
- setup/fedora.sh: require remote is Linux + has dnf (RPM-based)
- manage_runner.sh: native runner add/remove requires macOS
- run_all.sh: control plane must be macOS
- preflight.sh: 3 new checks (1: local=macOS, 2: Unraid=Linux, 3: Fedora=Linux+dnf)
- phase5_migrate_pipelines.sh: fix sed -i to be portable (no macOS-only syntax)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

run_all.sh

@@ -16,6 +16,11 @@ set -euo pipefail
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 source "${SCRIPT_DIR}/lib/common.sh"
 
+# ---------------------------------------------------------------------------
+# OS check — the control plane must be macOS (uses brew, launchctl, macOS sed)
+# ---------------------------------------------------------------------------
+require_local_os "Darwin" "run_all.sh must run from macOS (the control plane)"
+
 # ---------------------------------------------------------------------------
 # Parse arguments
 # ---------------------------------------------------------------------------