fix(planning): name the replacement in an archived, superseded interview question's banner #8087

Refs: #7750

Agent Brief

Type: Bug
Summary: An archived question that was superseded shows one banner line naming its replacement.

Current behavior:
An archived question's detail banner shows the session's archived.why text. That is one batch sentence shared by every card archived together. A question with supersededBy can also show a separate Superseded banner.

Desired behavior:

• An archived question with supersededBy shows one banner line naming its replacement as a link, in place of the batch sentence. No second banner is added.
• An archived question without supersededBy shows archived.why as today.
• A superseded question that is not archived is unchanged.

Key interfaces:

• The question detail banner render for archived and superseded states.
• A question's supersededBy field and archived.why.

Acceptance criteria:

• The diff adds a UI check: an archived question with supersededBy renders exactly one banner, and that banner names and links the replacement id.
• The same check confirms that an archived question without supersededBy still shows its archived.why text.
• scripts/check-changelog-fragments.sh passes, with one planning patch fragment added.
• CI's test-bash passes on the PR.

Out of scope:

• The Groups rail (sibling item).
• Disabling controls on superseded questions (feat(planning): interview page does not enforce answer order or react to changed answers like the terminal interview #5796 G4).

Refs #7750

This was generated by AI during backlog shaping. Split from #7750 so each piece fits the lane's run time; the owner approved this split in an attended backlog-shaping session on 2026-10-18.