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/src/ui/main_tui/render.rs

@@ -17,18 +17,6 @@ use ratatui::{
     widgets::Paragraph,
 };
 
-const COMMAND_BAR_PREFIX: &str = "search: ";
-const MESSAGE_BAR_PREFIX: &str = "message (to: recipient text): ";
-const BROWSE_BAR_PREFIX: &str = "browse user: ";
-
-const fn command_bar_prefix(mode: CommandBarMode) -> &'static str {
-    match mode {
-        CommandBarMode::Search => COMMAND_BAR_PREFIX,
-        CommandBarMode::Message => MESSAGE_BAR_PREFIX,
-        CommandBarMode::Browse => BROWSE_BAR_PREFIX,
-    }
-}
-
 impl MainTui {
     pub(super) fn render(&mut self, frame: &mut Frame) {
         let mut constraints = vec![
@@ -458,7 +446,11 @@ impl MainTui {
     }
 
     fn render_command_bar(&self, frame: &mut Frame, area: Rect) {
-        let prefix = command_bar_prefix(self.state.command_bar_mode);
+        let prefix = match self.state.command_bar_mode {
+            CommandBarMode::Search => "search: ",
+            CommandBarMode::Message => "message (to: recipient text): ",
+            CommandBarMode::Browse => "browse user: ",
+        };
         let block = pane_block(true);
         // Derive from the block's inner rect so borders and padding stay in
         // one place; the cursor follows whatever the pane reserves.