feat: implement role management LiveViews

Add complete CRUD interface for role management under /admin/roles.

- Index page with table showing name, description, permission_set_name, is_system_role
- Show page for role details
- Form component for create/edit with permission_set_name dropdown
- System role badge and disabled delete button
- Flash messages for success/error
- Authorization checks using MvWeb.Authorization helpers
- Comprehensive test coverage (22 tests)

Routes added under /admin scope. All LiveViews load user role
for authorization checks. Form uses custom dropdown for permission sets.

lib/mv_web/live/role_live/index.html.heex

@@ -0,0 +1,91 @@
+<Layouts.app flash={@flash} current_user={@current_user}>
+  <.header>
+    {gettext("Listing Roles")}
+    <:subtitle>
+      {gettext("Manage user roles and their permission sets.")}
+    </:subtitle>
+    <:actions>
+      <%= if can?(@current_user, :create, Mv.Authorization.Role) do %>
+        <.button variant="primary" navigate={~p"/admin/roles/new"}>
+          <.icon name="hero-plus" /> {gettext("New Role")}
+        </.button>
+      <% end %>
+    </:actions>
+  </.header>
+
+  <.table
+    id="roles"
+    rows={@roles}
+    row_click={fn role -> JS.navigate(~p"/admin/roles/#{role}") end}
+  >
+    <:col :let={role} label={gettext("Name")}>
+      <div class="flex items-center gap-2">
+        <span class="font-medium">{role.name}</span>
+        <%= if role.is_system_role do %>
+          <span class="badge badge-warning badge-sm">{gettext("System Role")}</span>
+        <% end %>
+      </div>
+    </:col>
+
+    <:col :let={role} label={gettext("Description")}>
+      <%= if role.description do %>
+        <span class="text-sm">{role.description}</span>
+      <% else %>
+        <span class="text-base-content/50">{gettext("No description")}</span>
+      <% end %>
+    </:col>
+
+    <:col :let={role} label={gettext("Permission Set")}>
+      <span class={permission_set_badge_class(role.permission_set_name)}>
+        {role.permission_set_name}
+      </span>
+    </:col>
+
+    <:col :let={role} label={gettext("Type")}>
+      <%= if role.is_system_role do %>
+        <span class="badge badge-warning badge-sm">{gettext("System")}</span>
+      <% else %>
+        <span class="badge badge-ghost badge-sm">{gettext("Custom")}</span>
+      <% end %>
+    </:col>
+
+    <:action :let={role}>
+      <div class="sr-only">
+        <.link navigate={~p"/admin/roles/#{role}"}>{gettext("Show")}</.link>
+      </div>
+
+      <%= if can?(@current_user, :update, Mv.Authorization.Role) do %>
+        <.link navigate={~p"/admin/roles/#{role}/edit"} class="btn btn-ghost btn-xs">
+          <.icon name="hero-pencil" class="size-4" />
+        </.link>
+      <% end %>
+    </:action>
+
+    <:action :let={role}>
+      <%= if can?(@current_user, :destroy, Mv.Authorization.Role) and not role.is_system_role do %>
+        <.link
+          phx-click={JS.push("delete", value: %{id: role.id}) |> hide("#row-#{role.id}")}
+          data-confirm={gettext("Are you sure?")}
+          class="btn btn-ghost btn-xs text-error"
+          aria-label={gettext("Delete role")}
+        >
+          <.icon name="hero-trash" class="size-4" />
+        </.link>
+      <% else %>
+        <div
+          :if={role.is_system_role}
+          class="tooltip tooltip-left"
+          data-tip={gettext("System roles cannot be deleted")}
+        >
+          <button
+            class="btn btn-ghost btn-xs text-error opacity-50 cursor-not-allowed"
+            disabled={true}
+            aria-label={gettext("Cannot delete system role")}
+          >
+            <.icon name="hero-trash" class="size-4" />
+          </button>
+        </div>
+      <% end %>
+    </:action>
+  </.table>
+</Layouts.app>