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/common/yaak-rpc/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "yaak-rpc"
+version = "0.0.0"
+edition = "2024"
+authors = ["Gregory Schier"]
+publish = false
+
+[dependencies]
+log = { workspace = true }
+serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true }
+ts-rs = { workspace = true }