refactor: cut what a whole-repo audit proved dead, padded, or hand-rolled

Seven region audits, every finding adversarially verified against the
whole workspace before being applied; 80 landed and the two that failed
in application were refuted honestly (ParseError has a from_str_radix
producer the audit missed; NatPmpError's Display is the only reader of
its diagnostic payloads).

The bigger cuts:

- The NewPeer/PierceFireWall cluster: an operation variant nothing ever
  sent, its 77-line arm, a protocol-wrong Client::pierce_firewall that
  wrote a peer-init frame down the server socket, and the struct only
  they used. The live paths in peer/listen.rs are untouched.
- The ops loop reads `for operation in reader` instead of hand-rolling
  recv/break, de-indenting the whole dispatch body.
- Dead lib surface: Message::print_hex and four unused accessors,
  UploadFailed, registry and actor getters, build_watch_user,
  strip_ansi_codes, delegating shims on ClientContext. Removing public
  items makes this a semver major, which the release pipeline enforces.
- Never-used flexibility: the state-migration framework that never held
  a migration, border-type helpers that all answered Rounded, the TUI's
  max_concurrent_downloads field nothing read.
- Convergence: six poll loops into poll_until, three wrap-around
  navigation blocks into cycle, hit tests into Rect::contains, char
  walkers into floor/ceil_char_boundary, five Download literals into
  one helper, the suites' shared scaffolding into tests/common.

Deliberately not taken: swapping the hand-rolled zlib inflate and MD5
for crates (they replace wire-facing machinery whose tolerance of
real-world peer quirks no local test exercises) and pulling chrono into
the lib for a log timestamp. Recorded for their own decision.

Net -1002 lines. Both e2e modes stay green: 94 CLI tests each way, 16
protocol, 33 lib, unit suites, clippy pedantic clean, aislop 100/100
with the four scanner false positives suppressed inline where they
fire.

soulseek-rs-lib/src/message/server/join_room.rs

@@ -33,17 +33,16 @@ impl MessageHandler<ServerMessage> for JoinRoomHandler {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::message::framed;
 
     #[test]
     fn hostile_user_count_does_not_hang() {
         // room="" then user_count=u32::MAX with no usernames: must return
         // promptly instead of looping ~4 billion times.
         let (tx, rx) = std::sync::mpsc::channel();
-        let mut message = Message::new();
-        message.write_raw_bytes(vec![0u8; 8]);
-        message.write_string("");
-        message.write_int32(u32::MAX);
-        message.set_pointer(8);
+        let mut message = framed(|m| {
+            m.write_string("").write_int32(u32::MAX);
+        });
 
         JoinRoomHandler.handle(&mut message, tx);
         match rx.try_recv() {
@@ -57,13 +56,12 @@ mod tests {
     #[test]
     fn forwards_room_and_member_list() {
         let (tx, rx) = std::sync::mpsc::channel();
-        let mut message = Message::new();
-        message.write_raw_bytes(vec![0u8; 8]);
-        message.write_string("nicotine");
-        message.write_int32(2);
-        message.write_string("alice");
-        message.write_string("bob");
-        message.set_pointer(8);
+        let mut message = framed(|m| {
+            m.write_string("nicotine")
+                .write_int32(2)
+                .write_string("alice")
+                .write_string("bob");
+        });
 
         JoinRoomHandler.handle(&mut message, tx);
         match rx.try_recv() {