docs: migrate hook documentation and live audio examples

[codeacme17]

Parent

#73

What to build

Move every public audio Hook guide to Nextra with bilingual explanations and live examples. Readers should be able to understand the Hook contract, connect an audio source, observe state or visualization output, and release resources safely.

Acceptance criteria

• English and Chinese pages cover useFetchAudio, useOscilloscope, usePlayer, useSpectrogram, useVuMeter, and useWaveform.
• Each page documents inputs, return values, lifecycle expectations, error conditions, and source links.
• Live examples handle browser audio permission/start requirements and provide usable failure feedback.
• Starting, stopping, switching sources, and unmounting do not leave active audio nodes or animation work.
• All Hook routes pass static build and browser smoke checks.

Blocked by

• docs: scaffold a Nextra documentation site alongside IslandJS #79 — docs: scaffold a Nextra documentation site alongside IslandJS.