docs: migrate visualization and container documentation

[codeacme17]

Parent

#73

What to build

Give Nextra readers complete documentation and runnable examples for LFO, Light, Oscilloscope, Spectrogram, VU Meter, Waveform, and Card. Web Audio visualizations should demonstrate real input and cleanup behavior, not static placeholders.

Acceptance criteria

• English and Chinese pages exist for every visualization and container component.
• API tables and representative customization examples match the exported package.
• Audio-backed examples can start, stop, reconnect, and clean up without leaking nodes or animation work.
• Documentation-only NextUI components are replaced without introducing a second general-purpose UI framework.
• All visualization and container 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.