feat(daemon): wire protocol with a type-safe method vocabulary and a generated OpenRPC contract

Methods and events are enums built by one macro, so every consumer matches
exhaustively: adding a member is a compile error until the dispatcher, the
published schema, and the remote client all handle it. docs/openrpc.json is
derived from the DTOs rather than hand-written, and a test fails the build
when the checked-in copy drifts.

soulseek-rs/src/daemon/mod.rs

@@ -0,0 +1,7 @@
+//! The resident service: one logged-in session, controlled over a socket.
+
+/// Generates `docs/openrpc.json` from the wire types and checks it is current.
+/// Test-only: the published document is served at runtime by `include_str!`.
+#[cfg(test)]
+mod openrpc;
+pub mod proto;