refactor!: remove redundant compatibility layers

Use native browser and Tauri behavior instead of custom selector, dialog, and window-state implementations. Remove obsolete bridge, relay, asset, and dependency paths to keep the supported surface small.

BREAKING CHANGE: The Noctalia relay no longer accepts --agent, and the Tauri host no longer exposes the legacy load_agent command.

ui/src/workspace/useWorkspace.test.tsx

@@ -10,9 +10,6 @@ const mocks = vi.hoisted(() => ({
 
 vi.mock("@tauri-apps/api/core", () => ({ invoke: mocks.invoke }));
 vi.mock("@tauri-apps/api/event", () => ({ listen: mocks.listen }));
-vi.mock("@tauri-apps/api/window", () => ({
-	getCurrentWindow: () => ({}),
-}));
 vi.mock("./persistence", () => ({
 	legacyPreferences: () => ({}),
 	loadPresentation: async () => ({