feat(extensions): mirror DocxReview as IDocxReview

[Ank-KhoaHo]

Closes the structural lag the same day it opened. DocxReview reached nuget.org in 0.36.1, so the
extensions package can finally wrap it — that gap has gone stale nine times, and this is the first
time it was paid in a day.

IDocxReview and DocxReviewService mirror all four operations 1:1, byte[] for byte[] and
Stream for Stream. The Ank.DocToolkit floor moves to [0.36.1, ).

A third guard the project split had quietly narrowed

CLAUDE.md prescribes a 1:1 mirror check, and it read src/DocToolkit/{core}.cs — which after the
split matched nothing for DocxEditor, PdfEditor, WorkbookEditor, PresentationEditor or
DocxReview. Five of thirteen pairs. It is a glob now, and the new pair was added in the same
change as the interface, which is what that section requires.

That is the third: StreamOverloadTests' inventory, check-readme-coverage.py, and now this.

Tests that discriminate

Nine, each asserting something a passthrough would fail — the standard the DI suite already sets,
because these services are pure delegation and the real risk is a member wired to the wrong thing:

• Inspect reads a document that has review state, so a stub returning an empty report fails
  where a clean-document test would pass
• accept and reject are asserted on opposite outcomes, so one implementation cannot satisfy both
• RemoveComments is asserted to have removed them
• every guard is asserted to throw, which a member doing nothing would not

Fixtures are raw OpenXml, available transitively through Ank.DocToolkit — no new dependency.
They have to be: TrackChanges records nothing for the library's own edits, and there is no
comment-authoring API, so a fixture built through DocxEditor would assert against empty sets
forever while looking green.

Verified by sabotage, not by reading

sabotage	tests failed
RejectRevisions wired to AcceptRevisions	1
Inspect wired to a clean document	3
RemoveComments returns its input	2

DI coverage back to 100%/100%, the floor it is held at because an uncovered member here is a
member nobody checked was wired to anything.

One number removed

The extensions README said "fifteen injectable interfaces" while listing sixteen, and seventeen are
registered — stale by two before this change touched it. The list is what check-readme-coverage.py
verifies; the count was a claim nothing did, so it is gone rather than corrected.

Closes A66.