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/ui/backend.go

@@ -2,6 +2,9 @@ package ui
 
 import (
 	"context"
+	"time"
+
+	"github.com/rivo/tview"
 
 	"git.stinnesbeck.com/nils/arr-tui/internal/arr"
 	"git.stinnesbeck.com/nils/arr-tui/internal/radarr"
@@ -41,6 +44,8 @@ type backend interface {
 	search(ctx context.Context, term string) ([]result, error)
 	monitorModes() []monitorMode // nil if not applicable
 	add(ctx context.Context, r result, c addChoice) (id int, err error)
+	// interactive starts an interactive release search for a library item.
+	interactive(v *searchView, r result)
 }
 
 // --- Radarr ---
@@ -83,6 +88,13 @@ func (b radarrBackend) add(ctx context.Context, r result, c addChoice) (int, err
 	return created.ID, err
 }
 
+func (b radarrBackend) interactive(v *searchView, r result) {
+	m := r.(movieResult)
+	v.app.openReleases("Releases for "+tview.Escape(movieTitleYear(m.Movie)),
+		func(ctx context.Context) ([]arr.Release, error) { return b.c.Releases(ctx, m.ID) },
+		b.c.Grab)
+}
+
 // --- Sonarr ---
 
 type seriesResult struct{ sonarr.Series }
@@ -133,3 +145,21 @@ func (b sonarrBackend) add(ctx context.Context, r result, c addChoice) (int, err
 	})
 	return created.ID, err
 }
+
+func (b sonarrBackend) interactive(v *searchView, r result) {
+	s := r.(seriesResult)
+	v.app.SetMessage("Loading episodes…")
+	go func() {
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer cancel()
+		episodes, err := b.c.Episodes(ctx, s.ID)
+		v.app.post(func() {
+			if err != nil {
+				v.app.SetMessage("[red]Loading episodes failed: " + tview.Escape(err.Error()))
+				return
+			}
+			v.app.SetMessage("")
+			v.app.pickSeason(b.c, s.Series, episodes)
+		})
+	}()
+}