fix: #3607228 Match the countries grid to the design's four-across layout

The country cards on /countries rendered 3-across (col-lg-4/col-xl-4/col-xxl-4) at a fixed 420px card height, against golden's 4-across (col-md-3/equivalent) at the same 420px height. Same photo height, ~110px wider card, so every photo read as squat/cropped-short by comparison even though nothing was actually cut off pixel-for-pixel.

Verified: golden card is 306×420 (4 per row), this view rendered 416×420 (3 per row) before the fix, 306×420 (4 per row) after.

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