docs(hooks): document manual shell hook allowlisting

[Sworntech-dev]

Summary

• Adds a manual allowlisting note for ~/.hermes/shell-hooks-allowlist.json.
• Documents the expected approvals array format with event and command.
• Notes that path-keyed sha256 entries do not approve hooks and suggests verifying with hermes hooks list.

Validation

• git diff --check -- website/docs/user-guide/features/hooks.md

Docs-only change; runtime behavior is unchanged.

References #31482

[teknium1]

Merged via PR #49944 (docs salvage cluster 2). Your commit was cherry-picked onto current main with your authorship preserved in git log — rebase-merged so it lands under your name. Thanks for the contribution!