Derive grid column count from the width the list is given

[sandbranch]

Addresses part of the grid item of #6769 ("span list/grid view across whole area").

Problem

The number of grid columns comes straight from the stored zoom preference and never looks at how wide the window actually is, so a phone in portrait and a tablet in landscape both show the same three columns. onConfigurationChanged only ever clamps the count downwards:

if (isGridEnabled && columnsCount > maxColumnSize) {
    (recyclerView?.layoutManager as GridLayoutManager).spanCount = maxColumnSize
}

so rotating to landscape raises the limit but never adds a column.

Fix

Add a GridLayoutManager that works out its own column count from the width it is given during layout, and hand it a target column width instead of a column count. The target is a dimension resource (grid_item_default_width, 140dp), so it can be adjusted per screen size later without touching this code.

The width has to be read during layout. The display metrics are not a usable substitute: they describe the display rather than the space the list occupies, they are not yet meaningful while the view is being created, and during a rotation they can still describe the previous orientation. I tried them first and got a portrait grid laid out to the width of a landscape screen (7 columns instead of 3), which is what prompted the layout-time approach.

Pinch to zoom keeps working and is still persisted. It now sets how large the cells are rather than a fixed column count, so a zoom level chosen in portrait carries over to landscape instead of being lost.

Testing

Measured on real devices, with the resolved width and column count logged:

Device	Orientation	Before	After
Samsung S23 (384dp)	portrait	3	3
Samsung S23	landscape	3	6
Lenovo Tab P11 Pro 2nd gen (768dp)	portrait	3	5
Lenovo Tab P11 Pro 2nd gen (1280dp)	landscape	3	9

The 140dp default was chosen so that a phone in portrait stays at three columns, i.e. existing phone users see no change at all; only wider windows gain columns.