Make the home page's AS name search work (closes #151)

The AS Name Search card on the home page said the search was coming soon.
It now asks the new GET /api/v1/search/as?q=<text> and lists the matches
as links to their AS pages. asinfo.Search ignores case, returns the first
matches up to a limit in AS number order, and counts all matches. An
empty q answers 400.

When the database has no record of an AS, its page and /api/v1/as/{asn}
take its handle and description from asinfo and still list its prefixes.
They answer 404 only for an AS with no record, no asinfo entry and no
prefix. AS 0 means no known origin: it always answers 404, and the search
never lists it.

Model: opus-5-5

internal/database/database_internal_test.go

@@ -20,6 +20,7 @@ import (
 
 	"git.eeqj.de/sneak/routewatch/internal/config"
 	"git.eeqj.de/sneak/routewatch/internal/logger"
+	"git.eeqj.de/sneak/routewatch/pkg/asinfo"
 	"github.com/mattn/go-sqlite3"
 )
 
@@ -1699,6 +1700,86 @@ func TestGetASDetailsListsEachPrefixOnce(t *testing.T) {
 	}
 }
 
+// TestGetASDetailsOfASNotInDatabase asks for ASes that the database has no
+// record of, some with stored routes. Each gets the prefixes of its routes and
+// no seen times. One that the AS info lookup knows gets its handle and
+// description from it. An AS with no record, no lookup entry and no route is
+// ErrNoRoute. Before the fix an AS with no record got no prefixes, although
+// its routes were stored.
+func TestGetASDetailsOfASNotInDatabase(t *testing.T) {
+	t.Parallel()
+
+	db, err := New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("failed to create database: %v", err)
+	}
+	defer func() { _ = db.Close() }()
+
+	ts := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+
+	tests := []struct {
+		asn      int
+		listed   bool     // in the AS info lookup
+		prefixes []string // of the routes stored for the AS
+	}{
+		{15169, true, []string{"192.0.2.0/24"}},
+		{13335, true, nil},
+		{4200000000, false, []string{"198.51.100.0/24"}},
+	}
+
+	var routes []*LiveRoute
+
+	for _, tt := range tests {
+		if _, ok := asinfo.Get(tt.asn); ok != tt.listed {
+			t.Fatalf("AS%d in the AS info data: %t, want %t", tt.asn, ok, tt.listed)
+		}
+
+		for _, prefix := range tt.prefixes {
+			routes = append(routes, mkV4Route(t, prefix, tt.asn, ts))
+		}
+	}
+
+	err = db.UpsertLiveRouteBatch(routes)
+	if err != nil {
+		t.Fatalf("UpsertLiveRouteBatch: %v", err)
+	}
+
+	for _, tt := range tests {
+		got, prefixes, err := db.GetASDetails(tt.asn)
+		if err != nil {
+			t.Errorf("GetASDetails(%d): %v", tt.asn, err)
+
+			continue
+		}
+
+		want := ASN{ASN: tt.asn}
+		if info, ok := asinfo.Get(tt.asn); ok {
+			want.Handle, want.Description = info.Handle, info.Description
+		}
+
+		var gotPrefixes []string
+		for _, route := range prefixes {
+			gotPrefixes = append(gotPrefixes, route.Prefix)
+		}
+
+		if *got != want || !slices.Equal(gotPrefixes, tt.prefixes) {
+			t.Errorf("GetASDetails(%d) = %+v with prefixes %v, want %+v with %v",
+				tt.asn, *got, gotPrefixes, want, tt.prefixes)
+		}
+	}
+
+	const absentASN = 4200000001 // no record, no lookup entry and no route
+
+	if _, ok := asinfo.Get(absentASN); ok {
+		t.Fatalf("AS%d is in the AS info data", absentASN)
+	}
+
+	_, _, err = db.GetASDetails(absentASN)
+	if !errors.Is(err, ErrNoRoute) {
+		t.Errorf("GetASDetails(%d): error %v, want %v", absentASN, err, ErrNoRoute)
+	}
+}
+
 // TestASPrefixQueriesUseCoveringIndexes checks the plan of each query that
 // lists the prefixes an AS originates: a search of a covering index and no
 // temporary B-tree, so the list reads one index entry per prefix, not one