Add connection history per peer with country and network lookup

- The stats sampler records sessions per peer: start, end, address and
  traffic. A session ends when the peer goes quiet or is disabled; a new
  one starts when the device changes networks. Stored in stats.json and
  kept as long as the daily traffic history (max 1000 per peer).
- Country and network operator come from the free DB-IP Lite databases
  (CC BY 4.0), downloaded monthly and looked up locally, so peer
  addresses never leave the server. Settings → Data retention can switch
  this off, which deletes the databases.
- API: GET /peers/{id}/sessions; peer stats include the current location;
  settings include the database status.
- Web UI and iOS app: connection history card, location line, country
  code in the peer list (web), switch in data retention.

Claude-Session: https://claude.ai/code/session_01RAnLbyQZ5ZTA7KqwXP98nw

app.css

@@ -94,6 +94,7 @@ h1 { margin: 0; font-size: 26px; font-weight: 600; letter-spacing: -0.01em; over
 .pills { display: flex; flex-wrap: wrap; gap: 6px; }
 
 /* status */
+.cc { display: inline-block; margin-left: 6px; padding: 0 5px; border: 1px solid var(--line); border-radius: 4px; font-size: 11px; color: var(--ink-2); vertical-align: 1px; }
 .badge { display: inline-flex; align-items: center; gap: 6px; font-size: 12px; font-weight: 500; padding: 3px 10px; border-radius: 999px; background: #efefeb; color: #3d3e42; white-space: nowrap; }
 .dot { width: 8px; height: 8px; border-radius: 50%; background: #9a9b97; display: inline-block; flex: none; }
 .dot.ok { background: var(--good); }