feat: add knowledge base suggestion core

[nonggde]

Summary

• Add a folder-local Knowledge Base Suggestion core service with request/article validation, deterministic scoring, ranked suggestions, and UI-ready loading/empty/error/success state helpers.
• Add synthetic local article/request fixtures and a folder-local public API via index.mjs.
• Document the API contract, state shapes, fixtures, scoring model, and limitations without wiring into the main app.

Validation

• node --test tools/v2/team/knowledge-base-suggestion/tests/knowledge-base-suggestion.test.mjs
• API export smoke check passed for index.mjs
• git diff --check

Closes #610