fix: review findings on the protocol work

Correctness:
- A child that stopped reading could freeze the whole client: the relay
  writes under the context lock and the socket was blocking, so one stalled
  peer took every download, upload and API call with it. Child writes now
  have a deadline, and a child that hits it loses its slot.
- Relaying searches to children was gated by the leaf's answer budget, so a
  parent forwarded a fraction of the stream while advertising itself as
  healthy. The budget bounds our own share scan, which is what it was for;
  the tree's stream goes down whole.
- A dropped client kept its listener port for the life of the process, so a
  retried login advertised an ephemeral port nobody was told about. The
  listener is now stopped and the operations thread let go.
- Excluded phrases were compared against a lowercased path without being
  lowercased themselves, so a capitalised phrase never matched. They are
  normalised where they arrive.
- Losing our own operatorship wiped the room's whole operator roster,
  though we are still a member who can see it.
- A brokered ConnectToPeer of type D was logged and dropped; the peer is
  now told, since we never dial out to adopt a child.
- A peer request made with no server connection returned Ok and parked
  forever; it says NotConnected, as its docs always claimed.
- An empty interest was refused locally but still sent, leaving the
  server's list and ours permanently apart.

Simplification:
- Deleted the excluded-phrase helper nothing called, and the field doc that
  promised behaviour it never had.
- The four roster handlers and four standing handlers were eight
  constructors carrying constants their own message code already implies:
  one newtype each, 100 lines less.
- One place registers a search; the phrase list is borrowed, not cloned per
  relayed search.

soulseek-rs-lib/src/client/search.rs

@@ -59,19 +59,10 @@ impl Client {
     fn send_search(&self, query: &str, wishlist: bool) -> Result<()> {
         info!("Searching for {}", query);
 
+        let token = self.register_search(query)?;
         let Some(handle) = &self.server_handle else {
             return Err(SoulseekRs::NotConnected);
         };
-        let token = next_search_token();
-
-        self.context.write_safe()?.searches.insert(
-            query.to_string(),
-            Search {
-                token,
-                results: Vec::new(),
-            },
-        );
-
         let query = query.to_string();
         let _ = handle.send(if wishlist {
             ServerMessage::WishlistSearch { token, query }