feat(web): add chevron affordance and scope-badge slot to dropdown triggers

Dropdown openers were visually indistinguishable from ordinary buttons. A
trailing chevron now marks every dropdown trigger — both the shared
dropdown_menu component and the bespoke member-filter trigger — and an
optional badge slot lets a trigger show a status indicator beside its label.

lib/mv_web/components/core_components.ex

@@ -464,6 +464,9 @@ defmodule MvWeb.CoreComponents do
 
   slot :inner_block, doc: "Custom content for the dropdown menu (e.g., forms)"
 
+  slot :trigger_badge,
+    doc: "Optional badge rendered in the trigger after the label (e.g. a scope badge)"
+
   def dropdown_menu(assigns) do
     menu_testid = assigns.menu_testid || "#{assigns.testid}-menu"
 
@@ -498,6 +501,8 @@ defmodule MvWeb.CoreComponents do
           <.icon name={@icon} />
         <% end %>
         <span>{@button_label}</span>
+        {render_slot(@trigger_badge)}
+        <.icon name="hero-chevron-down" class="size-4" />
       </button>
 
       <ul