[Frontend] Add browser support and feature-detection matrix

## Problem
Camera, WebCrypto, service workers, wallet providers, and file APIs are not uniformly available across supported browsers.
## Acceptance criteria
- Supported browser versions and degraded behavior are documented.
- Runtime feature detection gates unavailable actions with clear guidance.
- No unsupported API is invoked during SSR.
- CI or automated browser tests cover the supported matrix and one degraded environment.

Start by locating the camera, WebCrypto, service-worker, wallet-provider, and file-API call sites, along with SSR handling and CI or browser-test configuration. Document supported browser versions and degraded behavior, gate unavailable actions with guidance, avoid unsupported APIs during SSR, and cover the matrix plus one degraded environment in automated tests.

Written by the indexing model from the issue text.