feat: implement selective routing for "scope_*" users

- Users with "scope_{name}" prefix are routed to upstreams where {name}
  is present in the "scopes" property (comma-separated).
- Strict separation: Scoped upstreams are excluded from general routing, and vice versa.
- Constraint: SOCKS upstreams and DIRECT(`use_middle_proxy =
false`) mode only.

Example:
  User "scope_hello" matches an upstream with `scopes = "world,hello"`

src/proxy/direct_relay.rs

@@ -45,7 +45,7 @@ where
     );
 
     let tg_stream = upstream_manager
-        .connect(dc_addr, Some(success.dc_idx))
+        .connect(dc_addr, Some(success.dc_idx), user.strip_prefix("scope_").filter(|s| !s.is_empty()))
         .await?;
 
     debug!(peer = %success.peer, dc_addr = %dc_addr, "Connected, performing TG handshake");