Disable reservations; subnet enable/disable buttons; page-head CSS fix

- A disabled reservation is kept but ignored: the client gets a pool
  address like any other (steward reservation disable|enable, buttons and
  a checkbox in the web UI). Schema migration 3.
- Subnets get Disable/Enable buttons on their page and in the list.
- A rule left without its selector in style.css broke the page heading's
  layout, so the New ... buttons sat cramped under the description.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/steward/subnets.go

@@ -330,7 +330,7 @@ func reservationCmd() *cobra.Command {
 				return err
 			}
 			return output(rs, func(w io.Writer) {
-				fmt.Fprintln(w, "ID\tIP\tMAC / CLIENT ID\tHOSTNAME\tSUBNET\tLEASE\tCOMMENT")
+				fmt.Fprintln(w, "ID\tIP\tMAC / CLIENT ID\tHOSTNAME\tSUBNET\tLEASE\tSTATE\tCOMMENT")
 				for _, r := range rs {
 					who := r.MAC
 					if r.ClientID != "" {
@@ -340,7 +340,11 @@ func reservationCmd() *cobra.Command {
 					if r.Lease != nil {
 						lease = "until " + r.Lease.End.Local().Format("Jan 2 15:04")
 					}
-					fmt.Fprintf(w, "%d\t%s\t%s\t%s\t%s\t%s\t%s\n", r.ID, r.IP, who, orDash(r.Hostname), orDash(r.SubnetName), lease, r.Comment)
+					state := "on"
+					if r.Disabled {
+						state = "disabled"
+					}
+					fmt.Fprintf(w, "%d\t%s\t%s\t%s\t%s\t%s\t%s\t%s\n", r.ID, r.IP, who, orDash(r.Hostname), orDash(r.SubnetName), lease, state, r.Comment)
 				}
 			})
 		},
@@ -374,12 +378,37 @@ func reservationCmd() *cobra.Command {
 				} else {
 					fmt.Fprintln(w, "Lease:\tnone now")
 				}
+				if r.Disabled {
+					fmt.Fprintln(w, "State:\tdisabled (ignored: the client gets a pool address like any other)")
+				}
 				if r.Comment != "" {
 					fmt.Fprintf(w, "Comment:\t%s\n", r.Comment)
 				}
 			})
 		},
 	})
+	for _, on := range []bool{true, false} {
+		on := on
+		verb, short := "disable", "Ignore a reservation, keeping it (the client gets a pool address like any other)"
+		if on {
+			verb, short = "enable", "Use a disabled reservation again"
+		}
+		cmd.AddCommand(&cobra.Command{
+			Use: verb + " RESERVATION", Short: short, Args: cobra.ExactArgs(1),
+			RunE: func(cmd *cobra.Command, args []string) error {
+				c, err := newClient()
+				if err != nil {
+					return err
+				}
+				disabled := !on
+				var resp api.MutationResponse
+				if err := c.Do(ctx(), "PATCH", "/reservations/"+url.PathEscape(args[0]), nil, api.ReservationInput{Disabled: &disabled}, &resp); err != nil {
+					return err
+				}
+				return report(&resp)
+			},
+		})
+	}
 
 	var hostname, clientID, comment, ip, mac string
 	var opts, unsetOpts []string