Fix awg-ctrl hanging on the torrent flag; log out on an expired session

The torrent flag was read inside loops over users rows (users/stats,
peers, metrics) and each read queried the config table. SQLite has a
single connection here, so the nested query waited for it forever: the
first stats request or Prometheus scrape locked awg-ctrl for good, and
the panel showed no users and timed out.

- the block setting is kept in memory (loaded at start, updated on
  save), so the flag never touches the database
- the set of flagged IPs is taken once before the query, not per row
- regression test: collectMetrics must finish with users in the table

Panel: a 401 from the panel itself (its JWT not accepted) now returns to
the login screen; a 401 relayed from a node's awg-ctrl does not.

internal/ctrl/metrics_test.go

@@ -0,0 +1,37 @@
+package ctrl
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/maeneko/forgetting/internal/logx"
+)
+
+// SQLite открыт с одним соединением: любой запрос в базу изнутри цикла по строкам users ждал
+// бы его вечно и намертво вешал awg-ctrl (так было в 0.4.2 с меткой торрента). Скрейп метрик
+// идёт раз в 15 с, поэтому зависание проявлялось сразу.
+func TestCollectMetricsNoDeadlock(t *testing.T) {
+	db, err := openDB(filepath.Join(t.TempDir(), "users.db"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 5; i++ {
+		db.Exec("INSERT INTO users (name, ip, pub_key, vpn_key) VALUES (?, ?, ?, 'vpn://x')", fmt.Sprintf("u%d", i), fmt.Sprintf("10.9.0.%d", i+2), fmt.Sprintf("pk%d", i))
+	}
+	s := &Server{db: db, iface: "awg1", log: logx.New(os.Stderr, t.TempDir())}
+	s.shaping = newShaping(s)
+	s.torrent = newTorrent(s)
+	done := make(chan error, 1)
+	go func() { _, err := s.collectMetrics(); done <- err }()
+	select {
+	case err := <-done:
+		if err != nil {
+			t.Fatal(err)
+		}
+	case <-time.After(3 * time.Second):
+		t.Fatal("collectMetrics завис: запрос в базу изнутри цикла по строкам")
+	}
+}