feat(series): multi-field search, sort-direction toggle, apply placement

Toolbar feedback round: the series search box now matches whatever the
main search matches for a group — series NAME, any book's AUTHOR, and
any book's TITLE inside the series (WHERE EXISTS per group-row, so
counts stay true); the separate author input is gone from the toolbar
(the author= param stays live for the JSON API and deep links). The
sort control becomes a base-key select (Date added/Name/Author/Books/
Progress/Last read) plus a chevron direction toggle that flips and
resubmits; sort/dir compose through ResolveSeriesSort (full registry
keys keep working for back-compat, unknown base keys fall to recent).
The search/apply button moved next to the search box as requested, and
default URLs stay clean (sort/dir only emitted once the user chooses).

cmd/server/tests/series_sort_filter_test.go

@@ -164,13 +164,49 @@ func TestSeriesSortAndFilter(t *testing.T) {
 		assert.Equal(t, []string{"Probe Zebra Series", "Probe Mango Series", "Probe Apple Series"}, renderedNames("&sort=bogus-key"))
 	})
 
+	t.Run("base sort + direction toggle composes registry keys", func(t *testing.T) {
+		// The toolbar sends base keys + dir; defaults apply when dir is
+		// absent, and both directions of every base key are reachable.
+		cases := []struct {
+			query string
+			want  []string
+		}{
+			{"sort=name", []string{"Apple", "Mango", "Zebra"}},             // name asc default
+			{"sort=name&dir=desc", []string{"Zebra", "Mango", "Apple"}},    // toggle flips
+			{"sort=books&dir=asc", []string{"Apple", "Zebra", "Mango"}},    // books desc default, flipped
+			{"sort=progress&dir=asc", []string{"Apple", "Zebra", "Mango"}}, // progress desc default, flipped
+			{"sort=author", []string{"Mango", "Apple", "Zebra"}},           // author asc default
+		}
+		for _, tc := range cases {
+			got := renderedNames("&" + tc.query)
+			require.Len(t, got, 3, tc.query)
+			for i, want := range tc.want {
+				assert.Contains(t, got[i], want, "%s: position %d", tc.query, i)
+			}
+		}
+	})
+
 	t.Run("name query filters", func(t *testing.T) {
 		assert.Equal(t, []string{"Probe Mango Series"}, renderedNames("&q=Mango"))
 		// ILIKE is case-insensitive and substring-shaped.
 		assert.Equal(t, []string{"Probe Mango Series"}, renderedNames("&q=mango"))
 	})
 
-	t.Run("author query filters on any book's author", func(t *testing.T) {
+	t.Run("multi-field query matches authors and book titles", func(t *testing.T) {
+		// Author of Mango is "Alpha One" — the query no longer needs the
+		// separate author box.
+		assert.Equal(t, []string{"Probe Mango Series"}, renderedNames("&q=alpha+one"))
+		// "Zebra Book 2" is a book TITLE inside the Zebra series: the
+		// series must surface for a title match too.
+		assert.Equal(t, []string{"Probe Zebra Series"}, renderedNames("&q=zebra+book+2"))
+		// Nothing matches anywhere.
+		assert.Empty(t, renderedNames("&q=nobody-nowhere"))
+	})
+
+	t.Run("author param (API back-compat) filters on any book's author", func(t *testing.T) {
+		// The toolbar no longer renders a separate author box (the
+		// multi-field q covers authors), but the param stays live for
+		// the JSON API and deep links.
 		assert.Equal(t, []string{"Probe Mango Series"}, renderedNames("&author=alpha"))
 		assert.Empty(t, renderedNames("&author=nobody"))
 	})