docs: add hooks guide covering permissions, auditing, and notifications

Add a use-case-oriented guide for session hooks that covers:
- Permission control (allow-lists, directory restrictions, ask-before-destructive)
- Auditing & compliance (structured audit logs, secret redaction)
- Notifications & sounds (desktop notifications, Slack webhooks, system sounds)
- Prompt enrichment (project metadata injection, shorthand expansion)
- Error handling & recovery (retry logic, friendly messages)
- Session metrics (duration, tool call counts, end reasons)

Includes multi-language examples (TypeScript, Python, Go, .NET) and links
to the existing API reference docs in docs/hooks/.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: patniko