Rework Dream Garden layers, planting and audio feedback

[alecu]

Dream Garden now paints three ordered layers: planted flowers below the players, smaller and dimmer flying accents/seeds above them, and a HUD above both. Gardens begin empty. A catch plants at the catching player's depth, on the side they last moved toward, displaced by 75% of their width; flowers drift inward at 8% of seed speed and retire at the centre. Golden seeds occasionally pulse on independent random timers.

The HUD shows RELAX while either player holds A, then slides outward over 450 ms on release. Music and bloom sounds start enabled; either player's X toggle shows NOISY/QUIET for two seconds, with repeated toggles extending the notice. Rest preserves flower depths and stops music. The cumulative checkpoints and game guide match the new mechanics.

Validation: all SDK tests passed (CPython, MicroPython, Node, mpy-cross and native renderer checks); 24 Dream Garden tests cover layering, planting, seam catches, drift, glow, timed audio feedback, both players, pool limits and scene transitions. Tested the finished game in the browser with the WebGL renderer. Website slides, captures and game download are updated in a companion PR.

Companion PR: ventilastation/website#20

Preview: game · slides.

QUIET (audio off) and NOISY (audio on) are centred five-character notices. They hold for two seconds, then slide outward past the rim over 450 ms. A new toggle restores the position and restarts the notice. RELAX uses the same exit animation. Tests cover interrupted exits and both players; the CPU renderer check confirms clean clipping past the rim.

Each player retains their own last nonzero steering direction after stopping. Opposite directions cancel and leave that memory unchanged. Before the first movement, planting defaults to LEFT. Tests cover repeated catches, both players, relaxed movement and angular seam crossings.