Changelog and Audit Rails

Purpose

Changelog and audit rails keep system changes traceable.

Current changelog table

Runtime/schema changes should write to `amv_changelog_entries` when a database changelog entry is required. Do not write new records to old changelog tables.

Root changelog

For code-level work, update the root `CHANGELOG.md` when the task requires it. Add addon-level changelog notes when the addon already owns a changelog and the change belongs there.

What to record

Record behavior changes, schema changes, route changes, permission changes, public target changes, and cleanup work that future developers may need to understand.

What not to record

Do not turn changelogs into diary entries. The changelog should explain what changed and why it matters, not how heroic the afternoon felt.