Microphone/camera capture works on macOS (WKWebView) and Windows
(WebView2) but fails on Linux with `NotAllowedError`. WebKitGTK ships
with `enable-media-stream` off and a default `permission-request`
handler that denies every request.
This reaches the underlying `webkit2gtk::WebView` from
`on_webview_ready` and enables `enable-media-stream`, then installs a
**deny-by-default** `permission-request` handler: a `UserMedia` request
is allowed only from a trusted app origin (`tauri://localhost` in prod,
the Vite dev origin in debug) **and** when it targets an audio/video
device — everything else is denied. No-op on macOS/Windows.
- `webkit2gtk` is pinned to the version wry already uses (`=2.0.2`) so
there's a single shared copy of the native binding.
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Signed-off-by: Beckley <mattcbeckley@gmail.com>
c9aa55505c