Add voice command support via Web Speech API

[KiIISo]

Implement voice recognition using the browser's Web Speech API to allow users to navigate repositories and trigger actions hands-free.

Planned commands:

• 'show repositories' — navigate to repo list
• 'open [repo name]' — open a specific repo's issues
• 'go back' — navigate back

References:

• MDN Web Speech API: https://developer.mozilla.org/en-US/docs/Web/API/Web_Speech_API