F10 SLICE-4: manual smoke checklist + README F10 section (#29)

Adds docs/MANUAL-SMOKE-F10.md (clean editor → edit → propose → ✓/✗ →
Annotations toggle → status-bar PUC-6 → theming → cleanliness) following the
F7/F9 smoke format. Adds the F10 "write left / review right" section to the
README feature list and notes F6's two-pane diff and F9's authorship view are
retained only as data layers, not separate user surfaces.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -14,7 +14,8 @@ catalog (a pure, key-free SDK call) in a notification and the
 Features shipped so far: F2 region-anchored threads (Feature #4), F3 live
 human/Claude attribution (Feature #6), F4 propose/accept diff flow
 (Feature #12), F5 cross-rung sidecar contract (Feature #14), F6 diff-view
-toggle (Feature #17).
+toggle (Feature #17), and F10 interactive review — **write left / review
+right** (Feature #29).
 
 ## Architecture
 
@@ -237,6 +238,30 @@ a plain PR revert with zero data migration.
 Design: `vscode-cowriting-plugin-content/specs/coauthoring-out-of-workspace.md`.
 Live smoke: [`docs/MANUAL-SMOKE-F8.md`](docs/MANUAL-SMOKE-F8.md).
 
+## F10 — Interactive review: write left / review right (Feature #29)
+
+A clean, **zero-annotation editor** on the left; the rendered preview on the
+right as the **single interactive review surface**. The editor carries no
+attribution tint, no in-editor proposal threads, and no diff — all review lives
+in the preview, toggled by the **Annotations** switch in its header (on by
+default). `Ctrl+Alt+R` opens **"Open Review Preview"**.
+
+In the on-state the preview shows **green = human / blue = Claude /
+strikethrough = deleted**, and surfaces each of Claude's pending F4 proposals as
+a blue `cw-proposal` block with **✓ / ✗** buttons: **✓** accepts (the
+replacement lands Claude-attributed via the seam and the baseline advances past
+it), **✗** rejects (the block vanishes, the document untouched). With no preview
+open, a status-bar indicator shows the pending-proposal count and opens the
+review when clicked. Toggle **Annotations** off for clean rendered markdown.
+Read-only, sealed webview, no new persistence (INV-32..34).
+
+F6's two-pane diff and F9's authorship view are **retained only as data layers**
+(the baseline the preview diffs against; the F3 attribution that colors it) —
+they are no longer separate user surfaces.
+
+Design: `vscode-cowriting-plugin-content/specs/coauthoring-interactive-review.md`.
+Live smoke: [`docs/MANUAL-SMOKE-F10.md`](docs/MANUAL-SMOKE-F10.md).
+
 ## Develop
 
 - `npm run watch` — rebuild on change.