enhance(#3783): audit-uat summary segments current-milestone vs archived debt (#4336)

* test(#3783): add failing coverage for audit-uat summary segmentation

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix(#3783): segment audit-uat summary into current_milestone and archived buckets

Additive: current_milestone/archived are new; total_items, total_files, parse_gap_files, by_phase, and by_category are unchanged.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* docs(#3783): add changeset fragment for audit-uat summary segmentation

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* chore(#3783): allowlist the new audit-uat-summary-segmentation test file

lint-test-file-count.cjs baselines the "audit" module (keyed off bin/lib/audit.cjs)
at 6 pre-existing files; this adds the new dedicated suite as a 7th, matching the
module's existing one-file-per-feature-slice precedent.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* test(#3783): fix phase/file number mismatch in the mixed-milestone fixture

The active phase fixture used dir "02-current" with file "01-UAT.md" — a
cross-phase stray per phase-id.cts's isPhaseArtifact/scopeToPhase (#3511),
so the file was silently excluded from the scan and current_milestone read
{files:0, items:0} instead of {files:1, items:1}. Confirmed by direct CLI
run against a hand-built fixture before recommitting. Renamed the file to
02-UAT.md to match its directory's phase number, matching every other
fixture in this suite.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* docs(#3783): backfill changeset PR number to 4336

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: sim <sim@local>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

.changeset/serene-newts-click.md

@@ -0,0 +1,7 @@
+---
+type: Added
+pr: 4336
+---
+**`query audit-uat` now segments its summary by milestone.** The JSON output adds `summary.current_milestone: {files, items}` and `summary.archived: {files, items, by_milestone}`, so a consumer can read current-vs-archived UAT/verification debt directly instead of re-deriving the `archived_milestone` filter itself. Existing fields (`total_items`, `total_files`, `parse_gap_files`, `by_category`, `by_phase`) are unchanged. (#3783)
+
+<!-- docs-exempt: internal JSON contract of the `query audit-uat` CLI verb, consumed by workflow .md files (progress.md, audit-fix.md) rather than end users; the pre-existing sibling fields (total_items, by_phase, by_category, parse_gap_files) this is additive to were never documented in docs/ either, and the maintainer's triage approval scoped this PR to the summary builder + tests only -->