[P2] The sprite-review pages render at retired scales, so art is vetted at the wrong aspect

Found by the adversarial review on PR #811.

src/preview.ts:45,79-80 uses const TILE = 12; // matching the game scale feel and const h = 44; (44 is exactly the retired FLOOR). preview.html is a shipped, screenshotted page whose job is showing room art at game proportions, and it now shows 12 x 44, which is 3.67 tiles per floor against a world of 4.5.

src/gallery.ts:61-63 has the same problem independently (tile 18, floor 52, so 2.9 tiles per floor). Pre-existing, and now further off.

This matters more than it looks: these are the pages an artist uses to judge room art, so any art vetted through them is vetted at the wrong aspect, which is the exact error the scale change exists to correct. Fix this BEFORE the room-density and palette work in the visual-parity GDD, or that work is judged against a lie.

Derive both from src/render/scale.ts rather than restating numbers.

Start with src/render/scale.ts to identify the current scale values, then inspect the constants in src/preview.ts and src/gallery.ts. Update both sprite-review pages to derive their tile and floor dimensions from the shared scale source, and verify that their rendered proportions match the current game aspect.