Firefox WebExtensions port

[BraedenBDev]

PointDev is Chrome-only (MV3). To avoid vendor lock-in perception and broaden reach, investigate porting to Firefox via WebExtensions API. Key areas to assess: webextension-polyfill compatibility, sidePanel API alternatives (Firefox sidebar), captureVisibleTab availability, Web Speech API support in Firefox.

This is a risk mitigation item for NLnet submission — reviewers may flag Chrome-only as a concern.