#882: pixel-exact Composition viewer at 100 % and above

Problem: the viewer blurred hard edges even at Full resolution and 100 %
(reported on Discord). The frame rect was centred without snapping to
physical pixels, so bilinear sampling blended neighbouring pixels at 1:1
(worst at 125 %/150 % display scaling); More Accurate also magnified
bilinearly, so 200 %+ and lower resolutions were smoothed; and Zoom In /
Zoom Out stepped in points, so at 125 % scaling they never reached 100 %.

Fix: snap the frame origin (and the ViewerMap overlays use) to the
physical pixel grid; magnify with nearest in both Zoom Quality modes
(CPU texture options and the GPU frame sampler), keeping the averaged
minification below 100 % (#417); the snapshot texture follows the same
options; Zoom In / Out step through screen-pixel magnifications.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/preferences.md

@@ -94,7 +94,9 @@ Commands (CLI, MCP, control channel):
   how much of a position motion path the viewer draws (all, none, N seconds or N keyframes
   around the current time)
 - `previews.showInternalWireframes`: outlines of the layers inside a selected collapsed precomp
-- `previews.zoomQuality`: Faster = nearest-neighbour viewer scaling, More Accurate = bilinear
+- `previews.zoomQuality`: Faster = nearest-neighbour viewer scaling, More Accurate = averaged
+  (bilinear, mipmapped) when the frame is shown below 100 %; magnified frames show their pixels as
+  blocks in both modes, and the frame sits on the physical pixel grid, so 100 % is exact
 - `previews.displayProfile`: the monitor's colour space for View ▸ Use Display Color Management
 - `appearance.useLabelColorForTabs`: Composition / Timeline tabs show the comp's label colour,
   Effect Controls / Properties the layer's