Add WITH, EXPLAIN, and LEFT JOIN to top keywords for suggestions

[rolandwalker]

Description

Add these keywords to favorites, on the basis that these are very common.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

No correctness or security issues found.

Potential test gap (low risk)

• No direct coverage that with or left join appear in top keyword suggestions (only explain order was adjusted). If you want explicit coverage, add a small completion test for those prefixes.