Add sound effects and an anime.js + PolyCSS board assemble/clear

[apresmoi]

Summary

Adds a sound layer and animated board transitions to VoxJong, built by combining anime.js with PolyCSS. Rebased on the latest main (includes the recent theme/rotation/centering fixes).

Animation — anime.js + PolyCSS (app.vue)

PolyCSS renders each tile as its own DOM element; anime.js drives their transforms:

• Start-of-game "assemble" — tiles rain in from off-screen with a gravity fall + settle bounce (anime.js inQuad + a keyframe bounce). A support-graph schedule ensures a tile only lands after the tiles beneath it have settled ≥250ms, so nothing lands on a moving surface; same-layer tiles rain at varied speeds.
• New Game "clear-out" — the current board sweeps off the bottom via a staggered anime.js animation, timed to the clear sound, then the new board rains in.
• Screen-space transform calibration so tiles fall straight down at any camera angle; the board is hidden until the first drop-in so an un-textured board never flashes; the clock starts only after the last tile lands.
• Cancellation/teardown via utils.remove; the support-graph scheduling is custom, anime.js runs the tweens.

Rendering (voxels.ts)

• Each tile's full-span side wall is emitted as a hidden face, so buried tiles fall as complete boxes during the intro while the at-rest exposed-face optimization is preserved.

Sound (useSound.ts)

Small Web Audio player (preloaded/decoded buffers, randomized variants):

• select/deselect, combine a pair, landing ticks during the intro, clear sweep, hint (glass ping), win (gem collect).
• Muted by default; a speaker toggle persists to localStorage. Audio only unlocks on a real gesture, never claims the audio session while muted (iOS-friendly), and the context is disposed on unmount.

Dev

• A dev-only Solve button (hidden in production) fast-forwards the guaranteed-solvable removal order to the final pair, for testing the win state.

Notes

• Adds one dependency: animejs@4 (~13 KB gzip).
• Respects prefers-reduced-motion; build + tests pass; assemble/clear/win/New Game flows verified.