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.go

@@ -1748,6 +1748,10 @@ func (d *Database) GetASDetails(asn int) (*ASN, []LiveRoute, error) {
 // GetASDetailsContext returns the AS and the prefixes it originates, the IPv4
 // ones first, each once with the time of its newest route. It makes two index
 // searches per prefix, however many peers carry the prefix.
+//
+// An AS that only the AS info lookup knows comes with its handle and
+// description, and without prefixes or seen times. An AS that neither the
+// database nor the lookup knows is ErrNoRoute.
 func (d *Database) GetASDetailsContext(
 	ctx context.Context, asn int,
 ) (*ASN, []LiveRoute, error) {
@@ -1765,7 +1769,14 @@ func (d *Database) GetASDetailsContext(
 		&asnInfo.LastSeen)
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
-			return nil, nil, fmt.Errorf("%w: AS%d", ErrNoRoute, asn)
+			info, ok := asinfo.Get(asn)
+			if !ok {
+				return nil, nil, fmt.Errorf("%w: AS%d", ErrNoRoute, asn)
+			}
+
+			return &ASN{
+				ASN: asn, Handle: info.Handle, Description: info.Description,
+			}, nil, nil
 		}
 
 		return nil, nil, fmt.Errorf("failed to query AS: %w", err)