* Line library folders up with the strategy grid

Folders used a fixed 232px Wrap with a 14px gutter while strategies use
a column grid that stretches to the window, so folder rows stopped short
of the right edge and never lined up with the strategy tiles below.
Folders now sit on the same columns and gutter, and each card fills its
column. The edit dialog's preview keeps its old width.

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

* Test that library folders share the strategy grid's columns

Renders FolderContent at two window widths and checks every folder card
sits on a strategy tile column, so a later gutter or column-count change
can't pull the two grids apart unnoticed. Fails on the old Wrap layout.

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

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