feat: migrate audio hooks and examples to Tone.js 15

[codeacme17]

What to build

Move the Echo UI audio layer to Tone.js 15 as an isolated migration. Components, Hooks, examples, and public types should continue to connect, render, schedule, stop, and dispose real Web Audio nodes correctly.

Acceptance criteria

• Player loading, playback, pause/stop, progress, source changes, and disposal work with Tone.js 15.
• Oscilloscope, waveform, spectrogram, and VU meter paths handle current analyser, meter, channel, and return-value APIs.
• Envelope and LFO scheduling behavior is verified against a real browser AudioContext.
• Unmounting and repeated start/stop cycles release nodes, listeners, timers, and animation frames.
• Public Tone-related types and dependency/externalization decisions are documented and covered by package-consumer tests.
• Interactive audio examples pass browser smoke checks without changing unrelated UI tooling.

Blocked by

• chore: establish a reproducible modernization baseline #75 — chore: establish a reproducible modernization baseline.