Add interactive release search (M6)

Release listing and grab in the shared arr client, a full-screen release
list (sort, hide rejected, rejection reasons, confirmation before grabbing
rejected releases; Usenet only), and a season/episode picker for Sonarr.
Overlays are now a stack so dialogs can open above the release list.
Add a fake Newznab indexer to the dev setup.

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

internal/radarr/radarr_test.go

@@ -148,3 +148,16 @@ func TestSearchMovie(t *testing.T) {
 		t.Errorf("body = %v", got)
 	}
 }
+
+func TestReleases(t *testing.T) {
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v3/release" || r.URL.Query().Get("movieId") != "7" {
+			t.Errorf("unexpected request %s", r.URL)
+		}
+		w.Write([]byte(`[{"guid":"g","title":"x","approved":true}]`))
+	})
+	rels, err := c.Releases(context.Background(), 7)
+	if err != nil || len(rels) != 1 || rels[0].GUID != "g" {
+		t.Fatalf("releases = %+v, %v", rels, err)
+	}
+}