Migration notes for akm v0.5.0

- New top-level surfaces: `akm wiki …`, `akm workflow …`, `akm vault …`, and `akm save`.
- If you tried the unreleased single-wiki LLM prototype, move to the new `akm wiki …` workflow.
- Removed from the prototype surface: `akm lint`, `akm import --llm`, `akm import --dry-run`, `knowledge.pageKinds`, and the old ingest/lint LLM prompts.
- Existing raw wiki-like content should be moved into `wikis/<name>/raw/` and then managed with the new wiki commands.
