refactor: resolve all lint findings

- remove 34 trivial restating comments (auto-fix)
- replace all 20 production .unwrap() calls with graceful handling:
  ?-propagation via LockPoisoned, unwrap_or_default on infallible
  conversions, let _ = on actor-channel sends, and a downloads_sender()
  helper in the TUI that also dedupes three channel-init blocks
- collapse nested if into match guard (clippy::collapsible_match)
- split client.rs (2275 lines) into a client/ module: connection,
  search, downloads, uploads, rooms, operations
- split ui/main_tui.rs (2027 lines) into a main_tui/ module: render,
  input, browse, rooms, downloads, search
- extract oversized functions: peer_actor/server_actor handle_message
  into per-message helpers, main() into init_logging/run_default_tui,
  download_selector and main_tui render into per-section helpers

Mechanical only, zero behavior change. Verified: clippy clean
(pedantic+nursery), fmt clean, 143 unit tests + 16 e2e tests against
soulfind pass, lint clean.

soulseek-rs-lib/src/message/mod.rs

@@ -57,10 +57,8 @@ impl Message {
 
         let chunks = data.chunks(BYTES_PER_LINE);
         for (i, chunk) in chunks.enumerate() {
-            // Print the offset
             print!("{:04x}  ", i * BYTES_PER_LINE);
 
-            // Print the hexadecimal part
             for j in 0..BYTES_PER_LINE {
                 if j < chunk.len() {
                     print!("{:02x} ", chunk[j]);
@@ -76,7 +74,6 @@ impl Message {
 
             print!("  ");
 
-            // Print the ASCII part
             let mut i = 0;
             for &byte in chunk {
                 i += 1;
@@ -101,7 +98,7 @@ impl Message {
         if self.data.len() < 8 {
             return 0;
         }
-        u32::from_le_bytes(self.data[4..8].try_into().unwrap())
+        self.data[4..8].try_into().map_or(0, u32::from_le_bytes)
     }
 
     #[must_use]