* Keep voice's preview card inside the notch

With the agent menu open over a long task, the card grew past the window
(the open office's height) and Start and Cancel were cut off. The card is
now capped at that height; the menu and the task box shrink first and
scroll. A new shot, voice-<size>-menu-long, renders the tallest case.

* Voice: an aura in place of the listening and working cards' words

The listening and working cards show only a glowing ring, drawn on the CPU
in aura.rs (Slint has no shaders). It follows LiveKit Agents UI's Aura
state table (Apache-2.0); the drawing is Hover's own, because LiveKit's
shader is under a non-resale licence. The ring is 66 DIPs and the Esc chip
is gone (the Esc key still cancels). Its colour is set in Settings → Voice
→ Aura colour (presets or any hex), saved as Voice.AuraColor.

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Co-authored-by: Kiro Agent <244629292+kiro-agent@users.noreply.github.com>
Co-authored-by: 4regab <4regab@gmail.com>