docs(ci): vale accept-list for domain terms; drop dead duplicate (bo-lzik)

[scbrown]

Why

The Docs workflow runs Vale (Style check) across all docs/book/src/ files on any doc change, so domain-term spelling false-positives in files unrelated to a PR turned the check red on every docs PR — e.g. #24 (bo-qlfu) had to be merged past a red Style check.

What

• Whitelist the 14 flagged domain terms in the canonical accept-list (.vale/styles/config/vocabularies/Bobbin/accept.txt): async, changeset, changesets, Clippy, commit, exclude_tag, knowledge_context, knowledge_query, kota, Quipu, reactively, rebase, upserted.
• Remove the dead duplicate .vale/styles/Vocab/Bobbin/accept.txt. Vale 3.x reads config/vocabularies/, not the v2 Vocab/ path — that file was vestigial and invited edits to the wrong list (the recurring-confusion root cause).
• Document the accept-list location and how to find flagged terms locally in contributing.md; fix the stale Vocab/ path in documentation-strategy.md.

Verification

Ran the exact CI tool (vale 3.13.1):

vale sync
vale --minAlertLevel error docs/book/src/
✔ 0 errors, 0 warnings and 0 suggestions in 75 files.

Confirmed lowercase entries are case-insensitive (async covers Async), so no redundant capitalized variants were added. markdownlint: code fences carry languages (MD040), docs/plans/** is in the lint ignore list.

Closes bo-lzik.