docs(70): queue the Live Window App overlay layer

Record the creator's Live-only, single-layer scope and distinguish it from the
existing session-scoped Capture Window backdrop pin. Include HWND lifecycle,
protected-window, visual-only, and duplicate-underlay boundaries.

Reference scan: Microsoft HWND capture item API and OBS Window Capture:
https://learn.microsoft.com/en-us/windows/win32/api/windows.graphics.capture.interop/nf-windows-graphics-capture-interop-igraphicscaptureiteminterop-createforwindow
https://obsproject.com/kb/window-capture-sources

TASKS.md

@@ -9,7 +9,7 @@
 
 **Creator ruling 2026-11-09 — finish the queue before the new features, gold pass always last.**
 
-`40·A/C/D → Move → 9·5 → 14 (remaining slices) → 66 → 67 → 68 → 69 → 36`
+`40·A/C/D → Move → 9·5 → 14 (remaining slices) → 66 → 67 → 68 → 69 → 70 → 36`
 
 The rule behind the two retirements below: **do not rebuild the platform's own surface.** Scheduling,
 publishing, moderation and channel management are YouTube's; the app owns capture → scene → sound →
@@ -31,6 +31,7 @@ output.
 | 67 | ☐ | **Per-event alert videos** — a clip per monetization event, falling back to the default | [`task-67`](TASKS/task-67-per-event-alert-videos.md) |
 | 68 | ☐ | **Editing while live** + first-run On-Air state matching the 1-2-3 screen | [`task-68`](TASKS/task-68-edit-while-live.md) |
 | 69 | ☐ | **Chat sample-preview toggle** — per-layer control to show/hide mock chat in the preview; real messages unaffected, never output | [`task-69`](TASKS/task-69-chat-preview-toggle.md) |
+| 70 | ☐ | **Window App layer** — capture one selected running app window as a visual layer over Live's game/display capture | [`task-70`](TASKS/task-70-window-app-layer.md) |
 | 36 | ☐ | **Gold pass** — the v1 gate: screens/layers audit (every control does something), native-Windows verification, branding-flash decision. Always the last unit | [`task-36`](TASKS/task-36-gold-pass.md) |
 | 34 | ❌ | **Scheduled streams — retired 2026-11-09.** YouTube owns scheduling *and* the reminder that makes it useful; the app neither creates nor displays scheduled broadcasts, and there is no value in a copy that can fall out of sync | [`decisions`](docs/ai/decisions.md) |
 | 50 | ❌ | **Publish recording — retired 2026-11-09.** YouTube Studio owns upload (resumable, quota-aware, and it explains rejections). In-app publishing would also widen the OAuth consent to whole-channel video management. The recording lands in the creator's folder; the app adds "Show in folder" instead | [`decisions`](docs/ai/decisions.md) |