Link views from the zone list, add breadcrumbs and view colours

The view shown in the zone list and on the zone page now links to that
view. The zone page and changeset page get breadcrumbs, and the zone list
keeps its filters in the address so going back restores them. Views can
be given a colour (Views > Edit, `jarl view color`, PUT /views/{id}/color)
so zones of the same view are easy to spot; the colour is UI-only, kept
outside changesets, and needs no deploy.

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

internal/api/types.go

@@ -41,7 +41,13 @@ type Record struct {
 // View is a view with its zone count.
 type View struct {
 	model.View
-	Zones int `json:"zone_count"`
+	Zones int    `json:"zone_count"`
+	Color string `json:"color,omitempty"` // web UI colour, see model.ViewColors
+}
+
+// ViewColor sets the colour the web UI shows a view in.
+type ViewColor struct {
+	Color string `json:"color"`
 }
 
 // ACL is an ACL with the objects that use it.