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/bin/test_net.rs

@@ -1,10 +1,9 @@
 use peerspeak::network::{
     gossip::IrohGossipState,
-    RoomState, PeerState, RoomEvent,
+    RoomState, PeerState,
 };
 use iroh::{Endpoint, endpoint::presets};
 use iroh_gossip::net::Gossip;
-use std::sync::Arc;
 use tokio::time::{self, Duration};
 
 #[tokio::main]