feat(podcasts): generic-surface exclusions — podcasts never render as books (task 1.3)

§9 / D3 / D13 / D15 / D16: podcasts-type libraries are excluded from
every generic book surface. Under RLS these are pure UX/type filters
(engine already hides other users' episodes); their job is preventing
episode grids in surfaces designed for books. The discriminator is the
denormalized media_items.library_type_name (IS DISTINCT FROM 'podcasts'
— NULL rows predate the column and stay visible).

SQL (queries.sql, marked '-- podcasts exclusion (plan §9)'):
ListMediaItems/ListMediaItemsSorted (All Books) · SearchMediaItems +
SearchMediaItemsUnified (generic search) · FacetCountsUnderFilters (all
14 arms) + the six Search*Values facet-suggestion queries ·
GetDistinctSeries + Count (series pages) · GetLibraryItems (collections
picker) · dashboard system sections (Continue Reading / Recently Added
/ Recently Read / Not Started) · GetPopularBooks + GetTopBooksByMinutes
(book rankings must not rank episodes).

Go: statistics summary counts episodes' sessions into time-spent (D15
keeps that) but skips them in BooksActive/BooksFinished — an episode is
not a book. OPDS filters podcasts libraries via one helper at all 7
library-walk sites (D16).

Templ: LibrarySwitcher skips podcasts entries and TotalMediaCount
excludes them — presentation-layer filter so every switcher consumer
(dashboard, collections, custom-section builder) is correct at once
(D13); podcasts surface via /podcasts only.

internal/services/statistics_service.go

@@ -296,6 +296,13 @@ func (s *StatisticsService) UserSummary(ctx context.Context, userID pgtype.UUID,
 		entry.Sessions++
 		summary.SessionCount++
 
+		// Podcast episodes (plan D15): sessions flow into time-spent
+		// (the minutes/pages/sessions math above already ran), but an
+		// episode is not a book — never enters BooksActive/BooksFinished.
+		if strings.EqualFold(strings.TrimSpace(sess.LibraryTypeName.String), "podcasts") {
+			continue
+		}
+
 		mediaUUID, err := uuid.FromBytes(sess.MediaItemID.Bytes[0:16])
 		if err == nil {
 			key := mediaUUID.String()