Docs: record the zoom box as TASK 52 and fix the task-numbering drift (Unit: zoom docs)

The zoom feature shipped without a task record while its index rows carried the
"TASK 51" label — which belongs to the webcam background effects (Remove + Blur).
For an honest catalogue and handoff:

- TASKS/task-52-zoom-box.md: feature provenance (creator-requested), the three
  2026-10-08 corrections (loupe -> anchored capture over the full composite drawn
  last -> never show the dim shading), shapes, implementation map, tests, DONE.
- TASKS.md: row 52 added (shipped); row 51 reworded — unblocked now that the
  zoom build shipped.
- TASK 51 -> TASK 52 in Models/index.md, ViewModels/index.md, and the two code
  comments that pointed at the zoom as "TASK 51".
- HANDOFF.md: pre-push readiness notes (5 commits ahead, push-safe).

HANDOFF.md

@@ -1,8 +1,16 @@
-# HANDOFF — 2026-10-08 (zoom rework + dims-shading fix)
+# HANDOFF — 2026-10-08 (zoom box shipped, READY FOR PUSH)
 
 ## Branch
 - main (no feature branch)
 
+## Push readiness
+- **5 commits ahead of origin/main, clean to push** (fetch confirmed origin has not moved):
+  `966e718` zoom box visuals → `4b3d82f` zoom as layered + TASK 51 booking → `6bff21b`
+  anchored-capture rework → `948dd08` dims-shading fix → (docs unit: TASK 52 record +
+  numbering fixes + this HANDOFF).
+- The pinned-chat work unit below is **uncommitted on purpose** — `git push` sends only
+  commits, so pushing is safe; the dirty files stay local.
+
 ## Dirty files (NOT mine — the in-flight "pinned chat" work unit; do NOT commit or co-edit)
 - `Models/YouTube.cs`
 - `ViewModels/MainViewModel.Chat.cs`
@@ -25,6 +33,9 @@ is dimmed". Structural invariant added to `ZoomBoxInteractionTests`: `DimRectsLa
 child of `PreviewCanvas`, not inside `CanvasGrid`, and renders below the `ZoomBox`.
 
 ## Zoom feature state
+- **TASK 52 (zoom box) is now a first-class record** — see [`TASKS/task-52-zoom-box.md`](TASKS/task-52-zoom-box.md):
+  feature provenance + the three creator corrections, shapes, implementation map, tests.
+  TASK 51 (webcam background Remove + Blur) is unblocked for the next unit.
 - Models: `ZoomState.cs`, `ZoomShape.cs` (Circle/VerticalRectangle/HorizontalRectangle), `ZoomSceneElement.cs`.
 - ViewModel (`MainViewModel.Zoom.cs`): `ActivateZoom`/`ToggleZoom`/`DismissZoom`/`StartZoomMove`/`UpdateZoomMove`/`EndZoomMove` + `RebuildDimRectsForZoom`; transient element healed/mirrored by `HealZoomLayers`/`EnsureZoomLayer`.
 - Output: box composited last via `BlitZoom`/`ZoomMagnifier`; output crop = tier (box never the crop).