fix(husky): re-exec pre-push under bash for sh compatibility

Husky v9 invokes hooks via `sh -e` regardless of the script's shebang,
causing `set -o pipefail` and bash regex `[[ =~ ]]` in .husky/pre-push
to fail with "Illegal option -o pipefail" on systems where /bin/sh is
not bash (Debian/Ubuntu dash).

Add a POSIX-compatible preamble that re-execs the script under bash
when invoked without BASH_VERSION. No changes to gate logic.

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.husky/pre-push

@@ -1,4 +1,10 @@
 #!/usr/bin/env bash
+# Husky v9 invokes hooks via `sh -e` (see .husky/_/h), ignoring this shebang.
+# Re-exec under bash so `set -o pipefail` and `[[ ... ]]` below work portably.
+if [ -z "${BASH_VERSION:-}" ]; then
+  exec bash "$0" "$@"
+fi
+
 set -euo pipefail
 
 # Protected branches keep the full CI parity gate.