Add transport-agnostic RPC layer for proxy app

Introduces yaak-rpc (shared RPC infrastructure) and yaak-proxy-lib
(proxy app logic decoupled from any frontend). A single Tauri command
dispatches all RPC calls through a typed router, with TypeScript types
auto-generated via ts-rs and a generic rpc() function for type-safe
calls from the frontend.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates-proxy/yaak-proxy-lib/bindings/gen_rpc.ts

@@ -0,0 +1,9 @@
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+
+export type ProxyStartRequest = { port: number | null, };
+
+export type ProxyStartResponse = { port: number, alreadyRunning: boolean, };
+
+export type ProxyStopRequest = Record<string, never>;
+
+export type RpcSchema = { proxy_start: [ProxyStartRequest, ProxyStartResponse], proxy_stop: [ProxyStopRequest, boolean], };