[task] Expand glossary for contributor workflow labels

[phongndo]

Area

Docs

Goal

Add glossary entries for the labels and issue-claim terms new contributors see on the board.

Why this matters

University contributors should not need prior open-source experience to understand labels like help wanted, good first issue, or maintainer only.

Relevant files

• docs/glossary.md
• CONTRIBUTING.md if a cross-link is useful
• docs/maintainers.md only if a term must stay aligned with maintainer guidance

Depends on

None. This can be claimed immediately.

Out of scope

• Do not change label names or automation.
• Do not rewrite the whole glossary.
• Do not add process rules that conflict with CONTRIBUTING.md.

Definition of done

• Glossary explains good first issue, good for beginner, good first design issue, help wanted, maintainer only, milestone, /assign, and /unassign.
• Entries are short and written for first-time contributors.
• Any cross-links point to the existing contributing or maintainer docs.

Verification

• pnpm format:prettier:check
• Manually review the rendered Markdown or GitHub preview for readability.

Contributor notes

This is a docs-only starter task with clear boundaries.