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>, which
searches the AS list built into asinfo, and lists the matches as links
to their AS pages. An empty q answers 400. asinfo.Search now ignores
case and returns its matches in AS number order.

A match can be an AS that the database does not hold yet. Its AS page
and /api/v1/as/{asn} now answer with its handle and description from
asinfo and no prefixes, instead of 404. Empty prefix lists in that JSON
answer are [] rather than null.

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 +1700,46 @@ func TestGetASDetailsListsEachPrefixOnce(t *testing.T) {
 	}
 }
 
+// TestGetASDetailsOfASNotInDatabase asks an empty database for an AS that the
+// AS info lookup knows, and gets its handle and description with no prefixes
+// and no seen times. An AS that the lookup does not know is ErrNoRoute.
+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() }()
+
+	const knownASN, unknownASN = 15169, 4200000000
+
+	info, ok := asinfo.Get(knownASN)
+	if !ok {
+		t.Fatalf("AS%d is not in the AS info data", knownASN)
+	}
+
+	got, prefixes, err := db.GetASDetails(knownASN)
+	if err != nil {
+		t.Fatalf("GetASDetails(%d): %v", knownASN, err)
+	}
+
+	want := ASN{ASN: knownASN, Handle: info.Handle, Description: info.Description}
+	if *got != want || len(prefixes) != 0 {
+		t.Errorf("GetASDetails(%d) = %+v with prefixes %+v, want %+v and none",
+			knownASN, *got, prefixes, want)
+	}
+
+	if _, ok := asinfo.Get(unknownASN); ok {
+		t.Fatalf("AS%d is in the AS info data", unknownASN)
+	}
+
+	_, _, err = db.GetASDetails(unknownASN)
+	if !errors.Is(err, ErrNoRoute) {
+		t.Errorf("GetASDetails(%d): error %v, want %v", unknownASN, 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