Topic evidence previews: citations + lazy load in admin

[AndreRobitaille]

Summary

Improve admin topic previews to emphasize evidence and reduce load, aligning with Topic Governance.

Scope

• Fix highlight styling in preview text.
• Lazy-load previews on toggle to avoid preloading all rows.
• Show document type + page number as citations where available.

Requirements

• Preview length adjustable via parameter with max cap.
• Only topic name links to the detail page in admin list.
• Default admin topic sort remains last_seen_at desc.

Acceptance criteria

• Preview highlights are visible.
• Admin index loads fast (previews fetched only on toggle).
• Previews show source type + page when available.

[AndreRobitaille]

Status update (2026-02-07)

• Previews are showing correctly on both admin detail and index pages.
• Default sort set to Last Seen (desc), and only topic name links to detail.
• Preview length configurable via preview_window param.
• Index preview toggles work after adding row_toggle controller (asset precompile needed).

Remaining todos

1. Highlighting in preview text is not visible (preview text stays italic, highlight styling not applied).
2. Index previews are preloaded for all rows; should lazy-load previews on toggle instead.

[AndreRobitaille]

Done — closing as implemented.

Admin topic index (app/views/admin/topics/_topic.html.erb) has:

• Toggle-able preview row via a Stimulus row-toggle controller (data-action="row-toggle#toggle").
• topic_mention_preview helper renders highlighted terms + document type + page number when available.
• Preview window is parameterized (@preview_window).
• Topic name is the only detail-page link in the list row.
• Default sort remains last_seen_at desc (active scope).

One minor caveat: previews are rendered inline (hidden) rather than fetched-on-toggle via Turbo Frame. If admin list load time ever becomes a problem at scale, converting to lazy frames is a one-partial change — file a new issue then.