Monitor: 7 and 30 day views, traffic used, merged tiles

- ranges 7d (30 min step) and 30d (2 h step); Prometheus keeps 31d
- rate() window is at least the step, so long views show averages
  instead of a 2-minute sample; "now" values still use a 2m window
- overview returns used_down/used_up: increase() of the interface
  counters over the whole range
- tiles merged: traffic (with volume for the period), devices, load

cli/src/monitor.ts

@@ -20,7 +20,7 @@ export const MONITOR_HASH_FILE = `${AWG_DIR}/monitor_token.sha256`;
 const DEFAULTS_FILE = "/etc/default/prometheus";
 const MARKER  = "# managed by forgetting";
 const LISTEN  = "127.0.0.1:9090";
-const RETENTION = "15d";
+const RETENTION = "31d";   // с запасом на вид «30 дней» во вкладке «Монитор»
 
 const log  = (s: string) => console.log(`  ${s}`);
 function fail(s: string): never { console.error(`\n  ✗ ${s}\n`); process.exit(1); }