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/mod.rs

@@ -42,11 +42,16 @@ pub struct PeerSpeakTicket {
     pub topic_id: [u8; 32],
 }
 
-impl ToString for PeerSpeakTicket {
-    fn to_string(&self) -> String {
-        let serialized = serde_json::to_vec(self).unwrap();
-        // Convert to base64 URL-safe string
-        base64::Engine::encode(&base64::engine::general_purpose::URL_SAFE_NO_PAD, &serialized)
+impl std::fmt::Display for PeerSpeakTicket {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        // serde_json on a struct of String/[u8;32] fields is infallible in practice,
+        // but Display can't surface an error, so fall back to an empty ticket body.
+        let serialized = serde_json::to_vec(self).unwrap_or_default();
+        let encoded = base64::Engine::encode(
+            &base64::engine::general_purpose::URL_SAFE_NO_PAD,
+            &serialized,
+        );
+        f.write_str(&encoded)
     }
 }