feat(series): sort and filter the series page

The /series page rendered its grid in one fixed order (newest first)
with no way to find a series beyond eyeballing cards. The page now has
a toolbar — series-name search, author filter, viewer-progress filter
and a 12-key sort select — wired as a plain GET form (the page's
existing model: the URL is the single source of truth, and the library
switcher now carries q/author/status/sort along on switch).

Extensibility is deliberate (user request): sorts live in a registry
(services.ResolveSeriesSort) mirrored by a CASE cascade in
GetDistinctSeries and a <select> in series.templ — a new sort is one
entry in each. The sort value is a BOUND PARAM compared inside the
cascade, never interpolated; unknown keys resolve to the default.
Filters: series-name matches in WHERE (the group key, so counts stay
true); author (BOOL_OR any-book match) and status (finished/reading/
unstarted vs the viewer's progress, same 0.999 threshold as the
filter_query status arms) in HAVING so COUNT(*) keeps reporting the
whole series. GetDistinctSeriesCount shares the JOIN + HAVING so
pagination totals match. The reading_progress join can't multiply rows
(the table is UNIQUE per media_item+user).

Cards gain the viewer's finished-count ("X of N read" + progress bar),
and the empty state distinguishes "no series at all" from "no matches —
clear filters". The JSON /api/series endpoint takes the same params and
gains read_count/last_read_at additively.

Integration test pins every sort key against a three-series fixture
with distinct created/author/count/progress answers, the filter matrix,
composition, unknown-sort fallback, card read-counts and the JSON
contract — all as the fresh regular user so the live reader's data is
untouched.

internal/router/frontend.go

@@ -149,6 +149,25 @@ func registerFrontendRoutes(cfg *Config) {
 		}
 		offset := (page - 1) * perSeriesPage
 
+		// Series-page state (URL is the source of truth — plain GET form,
+		// no htmx on this page). Unknown values resolve to defaults in the
+		// service's registries, so hand-edited URLs stay safe.
+		state := templates.SeriesPageState{
+			Sort:   c.QueryParam("sort"),
+			Query:  c.QueryParam("q"),
+			Author: c.QueryParam("author"),
+			Status: c.QueryParam("status"),
+		}
+		opts := services.SeriesPageOptions{
+			Sort:   state.Sort,
+			Query:  state.Query,
+			Author: state.Author,
+			Status: state.Status,
+		}
+		if viewerID, vidErr := uuid.Parse(user.ID); vidErr == nil {
+			opts.ViewerUserID = uuidToPGType(viewerID)
+		}
+
 		var seriesCards []templates.SeriesCardData
 		totalPages := 1
 
@@ -162,7 +181,7 @@ func registerFrontendRoutes(cfg *Config) {
 			} else if libRes.LibUUID.Valid && !visibleSet[libRes.LibraryID] {
 				errorMsg = "Library not accessible"
 			} else {
-				seriesList, total, err := handlers.GetSeriesCardsData(c.Request().Context(), cfg.Queries, libRes.LibUUID, visibleIDs, perSeriesPage, offset)
+				seriesList, total, err := handlers.GetSeriesCardsData(c.Request().Context(), cfg.Queries, libRes.LibUUID, visibleIDs, perSeriesPage, offset, opts)
 				if err != nil {
 					log.Printf("GetSeriesCardsData failed: %v", err)
 					errorMsg = "Error loading series"
@@ -183,6 +202,7 @@ func registerFrontendRoutes(cfg *Config) {
 							BookCount:     s.BookCount,
 							TotalInSeries: s.TotalInSeries,
 							CoverPaths:    covers,
+							ReadCount:     s.ReadCount,
 						})
 					}
 				}
@@ -194,7 +214,7 @@ func registerFrontendRoutes(cfg *Config) {
 		}
 
 		var buf bytes.Buffer
-		err = templates.Series(user, seriesCards, libData, libraryID, totalPages, page, errorMsg).Render(c.Request().Context(), &buf)
+		err = templates.Series(user, seriesCards, libData, libraryID, totalPages, page, state, errorMsg).Render(c.Request().Context(), &buf)
 		if err != nil {
 			return err
 		}