Feat: support seeking with no audio loaded

[katspaugh]

Short description

Resolves #3298

Implementation details

If no audio is loaded but a waveform is rendered using pre-decoded peaks and duration, clicking on the waveform will now set the cursor to that position.

[github-actions]

ESLint Summary View Full Report

Annotations are provided inline on the Files Changed tab. You can also see all annotations that were generated on the annotations page.

Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	0	N/A

• Result: ✅ success
• Annotations: 0 total

---

^{Report generated by eslint-plus-action}