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/peer/download_peer.rs

@@ -380,10 +380,9 @@ impl DownloadPeer {
         status: DownloadStatus,
     ) {
         let _ = download.sender.send(status.clone());
-        client_context
-            .write()
-            .unwrap()
-            .update_download_with_status(download.token, status);
+        if let Ok(mut context) = client_context.write() {
+            context.update_download_with_status(download.token, status);
+        }
     }
 
     fn wait_while_paused(
@@ -491,7 +490,7 @@ impl DownloadPeer {
             let _ = dl.sender.send(DownloadStatus::Queued);
             client_context
                 .write()
-                .unwrap()
+                .map_err(|_| DownloadError::LockPoisoned)?
                 .update_download_with_status(dl.token, DownloadStatus::Queued);
         }