Add route age information to IP lookup API

- Add last_updated timestamp and age fields to ASInfo
- Include route's last_updated time from live_routes table
- Calculate and display age as human-readable duration
- Update both IPv4 and IPv6 queries to fetch timestamp
- Fix error handling to return 400 for invalid IPs

internal/routewatch/app_integration_test.go

@@ -190,11 +190,14 @@ func (m *mockStore) GetLiveRouteCounts() (ipv4Count, ipv6Count int, err error) {
 // GetASInfoForIP mock implementation
 func (m *mockStore) GetASInfoForIP(ip string) (*database.ASInfo, error) {
 	// Simple mock - return a test AS
+	now := time.Now()
 	return &database.ASInfo{
 		ASN:         15169,
 		Handle:      "GOOGLE",
 		Description: "Google LLC",
 		Prefix:      "8.8.8.0/24",
+		LastUpdated: now.Add(-5 * time.Minute),
+		Age:         "5m0s",
 	}, nil
 }