Support native convolve node #20

Parent: #4

Add renderer/native support for Elementary's convolve node.

Docs: https://www.elementary.audio/docs/reference/convolve

Scope:

• Confirm resource requirements for convolution impulse responses in Elementary.
• Integrate convolve with React Native audio resource loading/shared resources.
• Verify resource lifecycle behavior when impulse responses are loaded/unloaded.
• Add example or test coverage proving convolution works with bundled or document-directory audio resources.

Acceptance criteria:

• el.convolve can be used in React Native with a loaded impulse response resource.
• Missing/invalid resources fail predictably with useful errors.
• Resource cleanup does not leave stale shared resources in the native runtime.
• Works on both iOS and Android, or documents any platform limitation.