huddle: linux: grant WebKit user media requests

[brauliobo]

Summary

• enable WebKitGTK media-stream support when the Linux main webview is ready
• grant user-media permission requests only for Buzz's bundled UI and configured Vite development origin
• leave every other permission type and navigated origin to WebKit's default handling
• cover the trusted-origin boundary with focused unit tests

Root cause

WebKitGTK delegates getUserMedia permission decisions to the embedding application. Buzz did not handle WebKitUserMediaPermissionRequest, so WebKit denied microphone access without showing a prompt and Linux Huddles failed with NotAllowedError.

Impact

Linux users can acquire their microphone for Huddles while navigated or untrusted content remains unable to inherit user-media permission.

Closes #3495.

Validation

• cargo fmt --manifest-path desktop/src-tauri/Cargo.toml --all -- --check
• cargo test --manifest-path desktop/src-tauri/Cargo.toml webkit_permissions
• cargo check --manifest-path desktop/src-tauri/Cargo.toml
• cargo clippy --manifest-path desktop/src-tauri/Cargo.toml --all-targets -- -D warnings
• production-profile runtime test on Arch Linux, KDE Wayland, and WebKitGTK: Huddle microphone capture became active without the previous permission rejection

[Chessing234]

This is the missing piece for #3495-style Linux huddle failures. Handling WebKitUserMediaPermissionRequest only for the bundled UI / Vite origin is the correct trust boundary, and leaving other permission types alone avoids over-granting. Unit coverage on the trusted-origin check is welcome. One note for operators: this grants the permission request, but mic capture can still fail if PipeWire/GStreamer plugins are shadowed (see #3494) — worth cross-linking in the PR body so the two layers stay distinct.

[wpfleger96]

🤖 hey @brauliobo, thanks for this — your trusted-origin allowlist and the unit tests proving that boundary are the security core of what shipped: #3607 (just merged, fixes #3495) adopted the same origin check (tauri://localhost + dev origin) your PR pioneered, combined with a device-kind check. Closing this as superseded by the merged fix.