Several AudioWorklet demos have no way to stop playback except reloading the page

### Description
A number of demos under `src/audio-worklet/` only implement a **START** button. Once clicked, playback begins and the button disables itself there is no Stop control. The only way to stop the audio is to reload the page.

### Affected demos
- `src/audio-worklet/basic/handling-errors/`
- `src/audio-worklet/basic/message-port/`
- `src/audio-worklet/design-pattern/shared-buffer/`
- `src/audio-worklet/design-pattern/wasm-ring-buffer/`
- `src/audio-worklet/design-pattern/wasm/`

### Steps to reproduce
1. Open any of the demos above.
2. Click **START**.
3. Try to stop playback no control is available.

### Expected behavior
A visible **STOP** button should let the user suspend the audio
context and re-enable Start, without reloading the page.

### Proposed fix
Add a `button-stop` element next to `button-start` in each demo's markup, and wire it to `audioContext.suspend()`, re-enabling Start when clicked. Guard worklet-module loading and graph setup with flags so Start doesn't rebuild the audio graph on repeat clicks.

Start with the markup and start-button handlers in the five affected directories under src/audio-worklet/. Run one demo, trace its audioContext and worklet setup, then apply the same stop and repeat-start behavior across the listed demos. Done means each has a visible STOP control that suspends playback, re-enables START, and does not rebuild the graph on repeat clicks.

Written by the indexing model from the issue text.