Audit log UI for admin actions

## Summary
Implement an audit log UI for administrative and moderation actions with Discord-like traceability.

## Scope
- Display a filterable timeline of admin and moderation actions.
- Show actor, target, action type, time, and structured metadata where useful.
- Support the actions most important to a self-hosted operator first: permissions, channels, roles, invites, bots, and moderation.
- Provide enough detail to understand what changed without reading raw logs.

## Acceptance Criteria
- [ ] Authorized users can browse and filter audit events in the product UI.
- [ ] Events include enough structured context to answer who changed what and when.
- [ ] Sensitive actions such as permission and moderation changes are represented consistently.
- [ ] The audit log respects retention and visibility boundaries.

## Operational Notes
- Audit UI is a product surface; operators should not need shell access to understand routine admin actions.
- Event shape should remain stable enough for future export and API use.

The issue names no files, tests, or entry points; begin by locating the existing admin, moderation, and logging paths in the repository. Done means authorized users can filter a timeline showing who changed what and when, with consistent sensitive-action context and retention and visibility boundaries.

Written by the indexing model from the issue text.