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>

Cargo.toml

@@ -24,7 +24,6 @@ dirs = "6.0.0"
 iced = "0.14.0"
 iroh = "1.0.0-rc.0"
 iroh-gossip = "0.99.0"
-iroh-tickets = "1.0.0-rc.0"
 opus = "0.3.1"
 pipewire = "0.9"
 rand = "0.10.1"