fix(digest): drop archived followups from the due list

[atoz96]

archiving a followup page does nothing to vouch digest — it keeps appearing in the due list forever.

the asymmetry

the two queries sit adjacent in digest.build. the claim one filters lifecycle status:

for c in store.list_claims():
    if c.status in _RETIRED_CLAIM_STATUSES:
        continue

the page one doesn't:

due_pages = filter_pages(
    store.list_pages(),
    kind="followup",
    before={"due_at": now.date().isoformat()},
)

and it can't have — filter_pages only understands kind, equals, before, after. there is no status predicate anywhere in page_filters.py, so nothing in this path has ever excluded an archived page.

reproducing

two followup pages, same past due date, both followup_status: open, one ACTIVE and one ARCHIVED:

expected: ['fu-live']
actual:   ['fu-archived', 'fu-live']

_CLOSED_FOLLOWUP_STATUSES catches a followup that was marked done, but archiving the page is the other way to retire one, and that path was unguarded.

why it matters here specifically

the digest is the reviewer-facing briefing — vouch digest, kb.digest, and the SessionStart surface. an archived followup showing as overdue is worse than a stale search hit: it's an action item the reviewer is being asked to do something about, and the only way to make it go away was to edit followup_status, not to archive.

same shape as the retracted-claim gaps fixed in #581 and #624, and the archived-page gap in context packs — the lifecycle control is honoured on one read surface and ignored on the next.

the change

archived pages are filtered out before the kind/due-date predicates. i deliberately did not teach filter_pages about status: the digest is the caller that wants live pages only, and page_filters is a pure frontmatter matcher used by vouch pages and the CLI listing, where "show me archived followups" is a legitimate query. pushing status into the shared filter would change those callers too.

tests

test_build_excludes_archived_followups — fails on the previous code with

AssertionError: assert ['fu-archived', 'fu-live'] == ['fu-live']

verification

pytest tests/ -q --ignore=tests/embeddings   green
mypy src                                     Success: no issues found in 117 source files
ruff check src tests                         All checks passed!

[plind-junior]

Thanks for addressing the issue. LGTM!