chore: senior-review cleanup pass

- Remove Gemini's committed update_*.py regex-surgery scripts
- Drop unused iroh-tickets dependency (hand-rolled ticket is used instead)
- Replace ToString antipattern with Display impl on PeerSpeakTicket
- Route debug log to XDG state/cache dir instead of hardcoded /home path
- Clear all compiler + clippy warnings (unused imports, collapsible ifs,
  redundant pattern matching, missing Default)

Builds clean with zero warnings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/network/iroh_impl.rs

@@ -94,7 +94,7 @@ impl NetworkTransport for IrohTransport {
                 loop {
                     match conn_clone.read_datagram().await {
                         Ok(bytes) => {
-                            if let Err(_) = incoming_tx_inner.send((peer_id, bytes)).await {
+                            if incoming_tx_inner.send((peer_id, bytes)).await.is_err() {
                                 break;
                             }
                         }