Stage 17 (#15): admin users people/robots toggle + display-name & external-id glob filters

- account.ListUsers/CountUsers with a UserFilter: people vs robots (by a robot identity),
  case-insensitive '*'/'?' glob masks on display_name and any identity's external_id
- admin users list shows the real kind (robot/guest/registered), defaults to people,
  with a People/Robots toggle + a filter form; pager preserves the filter
- integration test for the filter; SQL verified against the live contour DB

backend/internal/adminconsole/views.go

@@ -50,6 +50,12 @@ type DashboardView struct {
 type UsersView struct {
 	Items []UserRow
 	Pager Pager
+	// Robots is the active people/robots toggle; NameMask/ExternalIDMask are the current
+	// glob filters; FilterQuery is those encoded for pager/toggle links.
+	Robots         bool
+	NameMask       string
+	ExternalIDMask string
+	FilterQuery    string
 }
 
 // UserRow is one account row in the list. MoveMin/Avg/Max are the account's