feat(podcasts): unset listening order defaults to reversed (audiobook-first)

The per-feed listening order — the Order dropdown on the podcast page
and player — resolved its UNSET state to "native": feed document order,
which runs newest-first for classic RSS. This platform is audiobook-
first, so native started every book at its LAST chapter (verified on
live data: 7th Son position 1 = Bonus Episode #2, positions descending
through the chapters).

The unset fallback flips to "reverse" at every resolution site of that
ONE setting — the podcast page's list + dropdown (podcastOrderForFeed),
the player's feed chain (reader.go), and the download queue
(orderOverrideFor) — so the dropdown shows reversed selected, the page
renders in that order, and play/download follow. Stored overrides are
untouched (native stays a valid savable choice); no ordering semantics
changed; collections are untouched.

Pins: the flipped native expectation is changelogged in contract_pins;
new pins cover the sequence config carrying reverse, feed position 1
playing last, and the page dropdown rendering reverse selected for an
unset feed.

cmd/server/tests/podcast_test.go

@@ -531,13 +531,31 @@ func TestPodcastPlayerOrderControl(t *testing.T) {
 	// match the escaped form.
 	esc := func(s string) string { return strings.ReplaceAll(s, `"`, """) }
 
-	t.Run("context_carries_feed_source", func(t *testing.T) {
+	t.Run("unset_default_is_reversed", func(t *testing.T) {
+		// 2026-11-01: the UNSET per-feed order resolves to "reverse"
+		// (audiobook-first — feed document order runs newest-first, so
+		// native started a book at its last chapter). The player's
+		// sequence config carries it; the podcast page's dropdown shows
+		// it selected; ep1 (feed position 1 of 2) plays LAST.
 		code, body := podcastAuthed(t, setup, setup.Token, "GET", ep1URL, "")
 		require.Equal(t, http.StatusOK, code)
 		assert.Contains(t, string(body), esc(`"source":"feed"`), "queue context must carry its owner (§10 R2)")
 		assert.Contains(t, string(body), esc(`"feed_id":"`+feedID+`"`))
-		assert.Contains(t, string(body), esc(`"order":"native"`))
-		assert.Contains(t, string(body), esc(`"episode_index":1`))
+		assert.Contains(t, string(body), esc(`"order":"reverse"`),
+			"unset order defaults to reversed (audiobook-first)")
+		assert.Contains(t, string(body), esc(`"episode_index":2`),
+			"feed position 1 plays last under the reversed default")
+	})
+
+	t.Run("podcast_page_dropdown_shows_reversed_when_unset", func(t *testing.T) {
+		code, body := podcastAuthed(t, setup, setup.Token, "GET", "/podcasts/"+feedID, "")
+		require.Equal(t, http.StatusOK, code)
+		html := string(body)
+		assert.Contains(t, html, `id="podcast-order-select"`, "the feed page renders its Order dropdown")
+		assert.Contains(t, html, `<option value="reverse" selected`,
+			"the unset default renders reversed as the selected option")
+		assert.NotContains(t, html, `<option value="native" selected`,
+			"native is no longer the unset default")
 	})
 
 	t.Run("order_dropdown_renders_feed_mode", func(t *testing.T) {