feat(daemon): expose watching over the RPC surface and the CLI

The watch subscription was reachable only from the library. It is most
useful against a daemon -- that is the session that stays connected long
enough to receive the server's status pushes -- so it needs the wire.

- proto: user.watch / user.unwatch / user.watched, with a Watched response
- SessionApi gains watch_user / unwatch_user / watched_users, so a local and
  a remote session are still interchangeable above the seam
- CLI: `watch add`, `watch remove`, `watch list`, documented in SKILL.md
  including the caveat that a one-shot run's watch ends with the run
- docs/openrpc.json regenerated from the wire types

soulseek-rs/src/commands/mod.rs

@@ -309,6 +309,7 @@ fn dispatch(ctx: &Ctx, command: Commands) -> CliResult {
             social::message_read(ctx, listen_span(duration, follow))
         }
         Commands::User(args) => peer::user(ctx, &args),
+        Commands::Watch(command) => peer::watch(ctx, &command),
         Commands::Whoami => peer::whoami(ctx),
         // main.rs runs these itself: some need no account, the rest need the
         // config store in scope. The arms only keep the match exhaustive.