Add the Flower Box wallpaper

[vaprdev]

A homage to the classic Flower Box screensaver: a glossy 3D object of six colored patches spins and bounces around a dark screen, morphing between a soft cube, a cluster of balls, a spiky star and a pinched pillow.

• Calm: one object, slow. Lively: faster, with the star. Teeming: three objects with faint trails.
• Dark teal by day, plum at sunset, navy-black at night; highlights take the patch color (cobalt glint at night), never white.
• Clicks knock an object away or pop in a small one; a finished agent races the morph and splits off copies; the easter egg is the old starfield warp.

Verified: typecheck, build, dev/check.ts flowerbox in octant and quadrant modes and --verify-dirty (0 failed, under 6 ms/frame), screenshots up to date.