Show the prefix page's origin names from the prefix query (closes #67)

The prefix page looked up each origin AS's details only for its handle and
description, and that lookup also reads every live route the AS originates.
GetPrefixDetailsContext already selects the handle and description; it now
returns them keyed by AS number, and the page uses them instead.

The origin list was handed each description but never rendered it; it now
shows it after the handle.

Model: opus-5-5

internal/database/database.go

@@ -1632,16 +1632,17 @@ func (d *Database) GetASPeersContext(ctx context.Context, asn int) ([]ASPeer, er
 }
 
 // GetPrefixDetails returns detailed information about a prefix
-func (d *Database) GetPrefixDetails(prefix string) ([]LiveRoute, error) {
+func (d *Database) GetPrefixDetails(prefix string) ([]LiveRoute, map[int]ASN, error) {
 	return d.GetPrefixDetailsContext(context.Background(), prefix)
 }
 
-// GetPrefixDetailsContext returns detailed information about a prefix with context support
-func (d *Database) GetPrefixDetailsContext(ctx context.Context, prefix string) ([]LiveRoute, error) {
+// GetPrefixDetailsContext returns the live routes for a prefix and, keyed by
+// AS number, the handle and description of each AS that originates it.
+func (d *Database) GetPrefixDetailsContext(ctx context.Context, prefix string) ([]LiveRoute, map[int]ASN, error) {
 	// Determine if it's IPv4 or IPv6 by parsing the prefix
 	_, ipnet, err := net.ParseCIDR(prefix)
 	if err != nil {
-		return nil, fmt.Errorf("invalid prefix format: %w", err)
+		return nil, nil, fmt.Errorf("invalid prefix format: %w", err)
 	}
 
 	tableName := "live_routes_v4"
@@ -1663,11 +1664,12 @@ func (d *Database) GetPrefixDetailsContext(ctx context.Context, prefix string) (
 
 	rows, err := d.db.QueryContext(ctx, query, prefix)
 	if err != nil {
-		return nil, fmt.Errorf("failed to query prefix details: %w", err)
+		return nil, nil, fmt.Errorf("failed to query prefix details: %w", err)
 	}
 	defer func() { _ = rows.Close() }()
 
 	var routes []LiveRoute
+	origins := make(map[int]ASN)
 	for rows.Next() {
 		var route LiveRoute
 		var pathJSON string
@@ -1690,13 +1692,18 @@ func (d *Database) GetPrefixDetailsContext(ctx context.Context, prefix string) (
 		route.IPVersion = ipVersion
 		route.MaskLength, _ = ipnet.Mask.Size()
 		routes = append(routes, route)
+		origins[route.OriginASN] = ASN{
+			ASN:         route.OriginASN,
+			Handle:      handle.String,
+			Description: description.String,
+		}
 	}
 
 	if len(routes) == 0 {
-		return nil, fmt.Errorf("%w: %s", ErrNoRoute, prefix)
+		return nil, nil, fmt.Errorf("%w: %s", ErrNoRoute, prefix)
 	}
 
-	return routes, nil
+	return routes, origins, nil
 }
 
 // GetRandomPrefixesByLength returns a random sample of prefixes with the specified mask length