Quest book map tab: keep the cursor visible

The zoomed map view resets the viewport to the full render size when done;
the HUD layer shifted that reset past the render target, SetViewport failed
and the map's 256x256 viewport stayed set, clipping the cursor. Full-width
viewports at x 0 are no longer shifted.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/hud.md

@@ -115,3 +115,14 @@ game lays them out at creation only).
 
 A window anchored `Screen` still counts as the outermost scope for events, so
 its child buttons (hooked as standalone controls, `Center`) don't shift again.
+
+## Viewports (cursor in the quest book, 2026-10-17)
+
+`SetViewport` inside a moved window is shifted like its vertices. The quest
+book's map tab ("V") draws the zoomed map view (`0x6cc950`), which sets a
+256x256 viewport and, when done, resets it to the full render size
+(`DxDriver7` `0x646510`: 0, 0, width x height). Shifted by the window's
+offset, that reset reached past the render target, `SetViewport` failed and
+the small viewport stayed set: the cursor (drawn after the UI) was only
+visible inside it. A viewport at x 0 across the whole render width is now
+passed unshifted.