Handle empty staged-file lists in generated hooks

[jmcte]

Problem statement

The generated pre-commit hook runs with Bash strict mode and dereferences an empty staged-file array. Metadata-only commits or hook invocations with no staged paths can therefore fail before the hook performs any useful validation.

Desired outcome

Generated hooks accept an empty staged-file list while preserving all existing environment-file protections.

Scope

• Expand the staged-file array safely when it is empty.
• Ignore the fallback empty entry.
• Add a generated-repository smoke test that invokes the hook with no staged files.

Acceptance criteria

• The generated pre-commit hook exits successfully on a feature branch with no staged files.
• Existing staged-file validation remains unchanged for non-empty entries.
• The full Bootstrap check suite passes.

Security implications

The change must not weaken the hook's rejection of committed environment files.

Documentation implications

None; this restores the documented hook behavior.