Docs search: find flags and codes, rank the changelog last, show passages #581

Summary

Make the docs search find flags and codes, stop the changelog crowding out the guides, and show the matching passage instead of a heading.

Context

At docs commit aeb5162:

• print-token returns no hits, though /cli names marfa login --print-token.
• soft delete trash returns /changelog first. The changelog is 11,854 words, the largest page; the next is 5,093.
• The first snippet of a hit is often the heading and not the passage. For rotate a key the first snippet is the text "Rotate a key".

All four search surfaces call src/lib/docs-tools.ts, so one change covers them.

Acceptance criteria

• A query for a flag (print-token), a snake_case code or a dotted name finds the page that contains it.
• The changelog ranks after any other page that matches equally.
• The first snippet of a hit is passage text, not a heading alone.
• Every query in the test from the pinned-queries sub-issue still passes.
• The JSON shapes of /api/docs/search and the MCP docs_search result are unchanged, and src/lib/mcp/server.test.ts passes.

Out of scope

• Embeddings or a second search system.

Notes

I did not check whether Orama's tokenizer can be configured through createFromSource in Fumadocs. If it cannot, say what is needed (a custom tokenizer, a pre-processing step, or a different Orama setup) before building.