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).

internal/services/series_service.go

@@ -4,6 +4,7 @@ import (
 	"bookhoard/internal/database"
 	"bookhoard/internal/utils"
 	"context"
+	"strings"
 
 	"github.com/google/uuid"
 	"github.com/jackc/pgx/v5/pgtype"
@@ -31,8 +32,9 @@ type SeriesInfo struct {
 // stale URL or hand-rolled API call can never reach the SQL with an
 // unhandled key.
 type SeriesPageOptions struct {
-	Sort         string // registry key, resolved by ResolveSeriesSort
-	Query        string // series-name substring
+	Sort         string // base toolbar key or full registry key
+	Dir          string // asc | desc ("" = the base key's default)
+	Query        string // multi-field: series name, author, or book title
 	Author       string // matches when ANY book's author matches
 	Status       string // "" | unstarted | reading | finished
 	ViewerUserID pgtype.UUID
@@ -65,12 +67,74 @@ var seriesStatusKeys = map[string]bool{
 	"finished":  true,
 }
 
-// ResolveSeriesSort maps any unknown/empty sort to the default. It is
-// the single source of truth backing both the SSR page and the JSON
-// API — the SQL CASE cascade must contain an arm for every key here.
-func ResolveSeriesSort(sort string) string {
+// seriesBaseSorts is the toolbar's base sort keys (the <select>) with
+// the direction each one STARTS in (the asc/desc toggle's initial
+// state). Composed with ResolveSeriesSort into the full registry keys
+// the SQL cascade implements.
+var seriesBaseSorts = map[string]string{
+	"recent":    "desc",
+	"name":      "asc",
+	"author":    "asc",
+	"books":     "desc",
+	"progress":  "desc",
+	"last_read": "desc",
+}
+
+// ResolveSeriesSort maps a sort value (either a FULL registry key like
+// "name_desc" — back-compat with old URLs and the JSON API — or a BASE
+// toolbar key composed with a direction) to the registry key the SQL
+// cascade implements, plus the EFFECTIVE direction (for the toggle's
+// arrow). Unknown values resolve to the default.
+func ResolveSeriesSort(sort, dir string) (string, string) {
+	sort = strings.TrimSpace(strings.ToLower(sort))
+	dir = strings.ToLower(strings.TrimSpace(dir))
+	if dir != "asc" && dir != "desc" {
+		dir = ""
+	}
+	// Full registry key straight from the URL wins as-is.
 	if seriesSortKeys[sort] {
-		return sort
+		return sort, seriesDirOf(sort)
+	}
+	base := sort
+	if base == "" {
+		base = "recent"
+	}
+	defaultDir, known := seriesBaseSorts[base]
+	if !known {
+		base, defaultDir = "recent", "desc"
+	}
+	if dir == "" {
+		dir = defaultDir
+	}
+	if base == "recent" && dir == "desc" {
+		return "recent", "desc"
+	}
+	return base + "_" + dir, dir
+}
+
+// seriesDirOf derives the display direction of a full registry key.
+func seriesDirOf(key string) string {
+	switch {
+	case strings.HasSuffix(key, "_asc"):
+		return "asc"
+	case strings.HasSuffix(key, "_desc"):
+		return "desc"
+	case key == "recent":
+		return "desc"
+	default:
+		if d, ok := seriesBaseSorts[key]; ok {
+			return d
+		}
+		return "desc"
+	}
+}
+
+// SeriesSortBase strips the direction suffix from a full registry key
+// ("name_desc" → "name") for the toolbar's base-key <select>.
+func SeriesSortBase(key string) string {
+	key = strings.TrimSuffix(strings.TrimSuffix(key, "_asc"), "_desc")
+	if _, ok := seriesBaseSorts[key]; ok {
+		return key
 	}
 	return "recent"
 }
@@ -95,7 +159,8 @@ func NewSeriesService(db *database.Queries) *SeriesService {
 // visibleLibraryIDs for an across-my-libraries page. Both filters compose:
 // the handler validates any explicit library_id against the visible set.
 func (s *SeriesService) GetSeriesPage(ctx context.Context, libraryID pgtype.UUID, visibleLibraryIDs []pgtype.UUID, limit, offset int, opts SeriesPageOptions) ([]SeriesInfo, int, error) {
-	sort := nargText(ResolveSeriesSort(opts.Sort))
+	sortKey, _ := ResolveSeriesSort(opts.Sort, opts.Dir)
+	sort := nargText(sortKey)
 	status := nargText("")
 	if seriesStatusKeys[opts.Status] {
 		status = nargText(opts.Status)