Widen the webhook page by half so an entrypoint URL fits on one line (closes #350)

The webhook page's maximum width goes from 72rem (1152 px) to 108rem (1728 px), half again as wide, so an entrypoint URL stays on one line in 1920- and 1440-pixel windows; the statistics pane and both columns widen with it. The title row now wraps, so a phone-width window no longer scrolls sideways.

The width is an inline style: static/css/style.css is linked by no page, and the committed Tailwind stylesheet has no class that wide. The webhook list, the event log, the navbar and the footer stay at 72rem.

Model: opus-5-5

internal/handlers/source_detail_test.go

@@ -241,3 +241,37 @@ func TestHandleSourceDetail_RendersNamedTargetFields(
 	assert.Contains(t, body, "(unavailable)")
 	assert.NotContains(t, body, "beak")
 }
+
+// TestHandleSourceDetail_FitsWideAndNarrowWindows pins the webhook
+// page's maximum width at 108rem (1728 px), half again the 72rem of
+// max-w-6xl that the webhook list and the event log use, so an
+// entrypoint URL fits on one line in a 1920-pixel window; and the
+// wrapping of its title row, so the buttons beside the title do not
+// push a phone-width window into scrolling sideways.
+func TestHandleSourceDetail_FitsWideAndNarrowWindows(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h    *handlers.Handlers
+		sess *session.Session
+		db   *database.Database
+	)
+
+	app := newTestApp(t, &h, &sess, &db)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+
+	body := renderSourceDetailPage(t, h, sess, wh.ID)
+
+	assert.Contains(
+		t, body,
+		`<div class="mx-auto px-6 py-8" style="max-width: 108rem"`,
+	)
+	assert.Contains(
+		t, body,
+		`<div class="flex flex-wrap justify-between items-center gap-2 mt-2">`,
+	)
+}