feat(cli): expose sharing, peer lookup and settings as one-shot commands

An agent driving the binary could search, fetch and chat, but it could not be
a peer: nothing kept a session online to serve files, nothing reported an
upload, shares could only be set at startup, and there was no way to ask
whether a peer was worth queueing to or to check credentials without doing
something else.

New commands:

  serve [--follow]                stay online sharing; one record per upload
  whoami                          credentials, connection and what we offer
  user <NAME>                     a peer's presence and share counts
  room users <ROOM>               the member roster
  shares list|add|remove|status|reindex
  config path|list|get|set

`config` and `shares list|add|remove` need no account, so they run before the
credential check — asking a script to log in for a `config get` would be a
poor trade. `serve` is the only place uploads are visible: they live in the
process serving them, so a one-shot `uploads list` could print nothing but an
empty list.

Library additions, all request/poll pairs matching the existing conventions:

- Client::room_members, kept current from the join and leave events
- Client::request_user_info / user_info, backed by new handlers for
  GetUserStatus (7) and GetUserStats (36) — codes the dispatcher previously
  logged as unhandled. The wire format is taken from soulfind's own source
  and pinned by an e2e test that asserts a peer's real share count.
- UserInfo carries presence and stats as Options, so a reply that never
  arrived cannot be read as "offline" or "shares nothing"
- request_user_info clears the previous answer, so the documented poll loop
  observes this request rather than the last one
- ServerMessage and ClientOperation are now #[non_exhaustive]: every protocol
  message the client learns adds a variant, and that should not break callers
- the crate root and prelude re-export every type a Client method returns

Also pins the output contract with tests: under --json, stdout carries only
newline-delimited JSON across fifteen command shapes while progress still
goes to stderr, and a failing command writes nothing to stdout at all.

soulseek-rs/src/commands/mod.rs

@@ -3,6 +3,8 @@
 //! Each command opens a [`Session`], does one job, writes records to stdout
 //! and progress to stderr, and returns an exit code through [`CliError`].
 
+pub mod peer;
+pub mod settings;
 pub mod social;
 pub mod transfer;
 
@@ -171,6 +173,9 @@ pub fn run(ctx: &Ctx, command: Commands) -> CliResult {
         Commands::Room(RoomCommand::Say { room, message }) => {
             social::room_say(ctx, &room, &message)
         }
+        Commands::Room(RoomCommand::Users { room, timeout }) => {
+            social::room_users(ctx, &room, Duration::from_secs(timeout))
+        }
         Commands::Room(RoomCommand::Listen {
             room,
             duration,
@@ -182,8 +187,15 @@ pub fn run(ctx: &Ctx, command: Commands) -> CliResult {
         Commands::Message(MessageCommand::Read { duration, follow }) => {
             social::message_read(ctx, listen_span(duration, follow))
         }
-        // Handled before credentials are required; see main.rs.
+        Commands::Serve(args) => peer::serve(ctx, &args),
+        Commands::User(args) => peer::user(ctx, &args),
+        Commands::Whoami => peer::whoami(ctx),
+        // These need no account, so main.rs answers them before asking for
+        // credentials; the arms exist only to keep the match exhaustive.
         Commands::Portmap => portmap(&ctx.out, ctx.settings.listen_port),
+        Commands::Config(_) | Commands::Shares(_) => {
+            Err(CliError::usage("handled without a session; see main::run"))
+        }
     }
 }