frontend: Improve /changes UX copy (commit/reject/undo)

[zhuamber370]

What

Review UI copy on /changes to make the governance flow clearer for first-time users.

Where to start (likely)

• Frontend page/components under frontend/ (search for "Commit" / "Reject" / "Undo")
• API docs for semantics: backend/README.md (changes/commits endpoints)

Why

Governed proposals are the differentiator. Clear labels reduce mistakes and support questions.

Suggested changes (examples)

• Clarify what Commit does (writes become permanent)
• Clarify what Reject does (discard proposal)
• Clarify what Undo last commit does (scope/limitations)

Acceptance criteria

• Copy changes only (no behavior changes)
• Screenshots before/after in PR
• English-first; keep terms consistent with README ("proposal", "commit", "audit", "undo")

Verification

• cd frontend && npm run build

Maintainer support

If you want to work on this but are unsure where the copy lives, comment on this issue and maintainers can point you to the exact files/components.