zeta2: Use bounded parallelism for tree-sitter indexing + await completion in zeta_cli (#39147)

Also skips indexing files that don't have a suffix that indicates a
known language, and skips when the language doesn't have an outline
grammar.

Release Notes:

- N/A

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Co-authored-by: Agus <agus@zed.dev>
773850f477Michael Sloan committed on 9/29/2025, 10:15:00 PM· committed by GitHubparent9c60bc3
15 files changedLine totals unavailable