feat(web): in-feed paste box + onboarding-aware connect confirmation

5b: connected users get a 'Summarize any video' URL input on the feed; submit
posts to /paste (HTMX) and swaps the resulting card / inline error into the feed.
7: the connect flash now sets expectations for the async onboarding burst —
'finding your subscriptions, your newest videos will appear below as summarized'.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/web/paste_test.go

@@ -1,6 +1,11 @@
 package web
 
-import "testing"
+import (
+	"bytes"
+	"context"
+	"strings"
+	"testing"
+)
 
 func TestParseYouTubeVideoID(t *testing.T) {
 	const id = "dQw4w9WgXcQ"
@@ -55,3 +60,21 @@ func TestParseYouTubeVideoID(t *testing.T) {
 		})
 	}
 }
+
+func TestListPageShowsPasteFormOnlyWhenConnected(t *testing.T) {
+	render := func(connected bool) string {
+		var buf bytes.Buffer
+		if err := ListPage(listBuckets{}, Filter{}, PipelineStats{}, "", connected).Render(context.Background(), &buf); err != nil {
+			t.Fatalf("render: %v", err)
+		}
+		return buf.String()
+	}
+
+	html := render(true)
+	if !strings.Contains(html, `name="url"`) || !strings.Contains(html, `action="/paste"`) {
+		t.Errorf("connected feed must show the paste form")
+	}
+	if strings.Contains(render(false), `name="url"`) {
+		t.Errorf("disconnected feed must not show the paste form")
+	}
+}