[refactor](trx-client): remove Qt/QML frontend support

Remove the Linux-only Qt/QML frontend (trx-frontend-qt) crate and all
references to it from the workspace, trx-client binary, configuration,
and documentation. This prepares for replacement with a native macOS
AppKit frontend.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

Cargo.toml

@@ -11,7 +11,6 @@ members = [
     "src/trx-client/trx-frontend",
     "src/trx-client/trx-frontend/trx-frontend-http",
     "src/trx-client/trx-frontend/trx-frontend-http-json",
-    "src/trx-client/trx-frontend/trx-frontend-qt",
     "src/trx-client/trx-frontend/trx-frontend-rigctl",
     "src/trx-core",
 ]