`--database` and `--db` read as one word abbreviated but take different
things, a configured name against a filesystem path, and they sit in
different positions: `haiku-rag --db /path info` fails with `No such option`.
The CLI already says "database" to the user everywhere it prints one, so the
name it selects by should say the same. Unreleased, so no deprecation.
Also: without a reranker, raise `search.limit` with the number of databases
searched, since each contributes its best matches to a list truncated back
to the limit.
Two files of 1,405 and 814 lines become seven: scope resolution, lifecycle,
search, documents, expansion, citations and capabilities. `_config`, `_seed`
and the rest move to `helpers.py`, importable by the sandbox tests that share
them, and the package points VCR back at `tests/cassettes/multi_db/`.
