Vacuum: pick up what you click, blow out what's in hand (t20)

A drag takes only the material it starts on (Shift: everything). The blow
selection is the hand: click or Q/E for one material, Ctrl+click for a mix.
Empty materials leave the hand, an empty hand blows nothing, and a pickup
fills an empty hand. Removes the pick-up marks and the F vacuum menu.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ui/previews.js

@@ -153,7 +153,7 @@ function drawPreviews() {
     if (t === 'vacuum') {
       // what the right button would blow, next to the cursor; what the left is sucking, while it sucks
       const sz = Math.max(6, zp * 1.6), qx = p.x + (r + 1.2) * zp, qy = p.y - (r + 1.2) * zp;
-      const swatches = GAME.lmb ? GAME.vacFilter >= 0 && GAME.collect.size ? [...GAME.collect] : [] : blowingAll() ? blowAllList() : blowList();
+      const swatches = GAME.lmb ? GAME.vacFilter > 0 ? [GAME.vacFilter] : [] : blowingAll() ? blowAllList() : blowList();
       swatches.slice(0, 4).forEach((m, k) => { ctx.fillStyle = rgbOf(m); ctx.fillRect(qx + k * (sz + 2), qy, sz, sz); });
       if (blowing || GAME.lmb) {
         // faint line from the nozzle: the path the grains take