Keep a trailing AS set out of the origin and the peerings (closes #75)

A path that ends in an AS set of several members, such as
[64496, 64497, [64498, 64499]], now has no origin: its route is stored
with origin 0 (none), and no member of the set is in a peering. A set of
one member counts as that AS. An announcement with an empty path is
still not stored.

ASPath keeps such a set apart from the sequence and gives the origin.
The prefix and AS handlers take the origin from it; the peering handler
uses the sequence only. The stored AS path still lists the set's members
at the end.

The prefix and prefix length pages show origin 0 as no known origin, the
IP lookup asks no WHOIS lookup for it, and the README says what it means.

Model: opus-5-5

internal/server/handlers_internal_test.go

@@ -331,6 +331,63 @@ func TestPrefixDetailShowsOriginNames(t *testing.T) {
 	}
 }
 
+// TestPagesSayOriginZeroIsNoKnownOrigin stores a route with origin 0, as the
+// prefix handler stores a route whose AS path ends in an AS set of several
+// members, and checks that the prefix page and the prefix length page say it
+// has no known origin, without a link to AS0 or the description of the
+// reserved AS 0 (https://git.eeqj.de/sneak/routewatch/issues/75).
+func TestPagesSayOriginZeroIsNoKnownOrigin(t *testing.T) {
+	t.Parallel()
+
+	db, err := database.New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("database.New: %v", err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	err = db.UpsertLiveRouteBatch([]*database.LiveRoute{{
+		ID: uuid.New(), Prefix: testPrefixV4, MaskLength: 24, IPVersion: 4,
+		OriginASN: 0, PeerIP: testPeerV4, ASPath: []int{64500, 64501, 64502},
+		NextHop: testPeerV4, LastUpdated: time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC),
+	}})
+	if err != nil {
+		t.Fatalf("UpsertLiveRouteBatch: %v", err)
+	}
+
+	reserved, ok := asinfo.Get(0)
+	if !ok {
+		t.Fatal("AS0 is not in the AS info data")
+	}
+
+	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	for _, path := range []string{"/prefix/" + testPrefixV4, "/prefixlength/24"} {
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, path, nil))
+
+		if rec.Code != http.StatusOK {
+			t.Fatalf("%s: status %d, want %d; body %s",
+				path, rec.Code, http.StatusOK, rec.Body)
+		}
+
+		page := rec.Body.String()
+
+		if !strings.Contains(page, "No known origin") {
+			t.Errorf("%s does not say the route has no known origin", path)
+		}
+
+		if strings.Contains(page, `href="/as/0"`) {
+			t.Errorf("%s links to AS0", path)
+		}
+
+		if strings.Contains(page, html.EscapeString(reserved.Description)) {
+			t.Errorf("%s shows AS0's description %q", path, reserved.Description)
+		}
+	}
+}
+
 // shortRequestDeadline is the deadline the tests below give a request. The
 // server's 30-second limit and the stats handlers' 4-second limit inherit it,
 // so the tests do not wait for either.