fix(daemon): ship the OpenRPC document inside the crate

docs/openrpc.json lived at the repository root, outside the soulseek-rs
package, so the include_str! in proto compiled from a checkout but not
from the published tarball - cargo publish failed verification and the
v13.0.0 release stopped after publishing the lib. The document moves
into the crate's own docs/, where packaging can see it; the generator
test and every link follow.

docs/daemon-protocol.md

@@ -2,7 +2,7 @@
 
 `soulseek-rs daemon` stays logged in and answers JSON-RPC over a socket, so
 several clients can share one Soulseek session. The machine-readable contract
-is [`openrpc.json`](openrpc.json), an [OpenRPC](https://open-rpc.org)
+is [`openrpc.json`](../soulseek-rs/docs/openrpc.json), an [OpenRPC](https://open-rpc.org)
 document and the JSON-RPC counterpart to OpenAPI. Point a client generator at it,
 or at a running daemon via `rpc.discover`, and you have a client in your
 language.