v0.55.0: the office list rises to the gold standard

The office list rises to the gold standard. The post and page list gains a triage filter layer and
self-describing rows, so a concept with a handful of entries reads as content rather than a few bare
titles.

Above the list, a triage bar filters by publish state in the admin's segmented check-and-tint
grammar: All, Pending edits (the entries on a cairn/ branch, whether branch-only or live with held
edits), and Published, each with a live count, plus an orthogonal Hidden toggle for the draft
entries. The counts come from the loaded set, so they are exact, and the filtering runs client-side
over the entries already in hand. Search composes with the active filter.

Each row now describes itself. A summary line sits under the title, drawn from the entry's
description or, lacking one, a short excerpt of its body. The Edited badge tints in the brand violet
as the one state to act on, mirroring the "Publish site (N)" count; Hidden reads as a de-emphasized
row with an eye-off tag rather than a competing badge; and the foot of the list carries a quiet
"New" row so a short list always shows its next step. A concept with no entries centers its empty
state on the page.

One data change feeds the rows: the content manifest now indexes a per-entry summary, built by the
same excerpt helper the public delivery already uses. Because the manifest is verified whole-string,
a site's committed manifest is stale until it is regenerated once.

Consumers must: regenerate the content manifest (npm run cairn:manifest or npx cairn-manifest,
then commit). The cairnManifest build fails closed until the regenerated manifest with the new
summary keys is committed.