feat: add GeoIP country lookup with embedded DB-IP Lite database (PLAN.md 4.3)

Embeds a DB-IP Lite country MMDB (~5MB) in the binary via go:embed,
keeping the single-binary deployment story clean. Country codes are
stored alongside login attempts and sessions, shown in the dashboard
(Top IPs, Top Countries card, Recent/Active Sessions, session detail).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/web/handlers.go

@@ -13,6 +13,7 @@ type dashboardData struct {
 	TopUsernames   []storage.TopEntry
 	TopPasswords   []storage.TopEntry
 	TopIPs         []storage.TopEntry
+	TopCountries   []storage.TopEntry
 	ActiveSessions []storage.Session
 	RecentSessions []storage.Session
 }
@@ -48,6 +49,13 @@ func (s *Server) handleDashboard(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	topCountries, err := s.store.GetTopCountries(ctx, 10)
+	if err != nil {
+		s.logger.Error("failed to get top countries", "err", err)
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return
+	}
+
 	activeSessions, err := s.store.GetRecentSessions(ctx, 50, true)
 	if err != nil {
 		s.logger.Error("failed to get active sessions", "err", err)
@@ -67,6 +75,7 @@ func (s *Server) handleDashboard(w http.ResponseWriter, r *http.Request) {
 		TopUsernames:   topUsernames,
 		TopPasswords:   topPasswords,
 		TopIPs:         topIPs,
+		TopCountries:   topCountries,
 		ActiveSessions: activeSessions,
 		RecentSessions: recentSessions,
 	}