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.

templates/utils.go

@@ -117,10 +117,10 @@ func MediaBadgeIcon(badge string) string {
 func TotalMediaCount(libs []LibraryData) int64 {
 	var total int64
 	for _, l := range libs {
-		// Unmounted storage contributes nothing visible: an offline
-		// library's holdings stay in the database but out of the UI
-		// until its folders return.
-		if l.Offline {
+		// Podcasts libraries are feed-managed (plan D13): not book-
+		// library inventory — excluded here so switcher totals stay
+		// consistent with the switcher's podcast-filtered option list.
+		if l.Offline || l.TypeName == "podcasts" {
 			continue
 		}
 		total += l.MediaCount
@@ -128,6 +128,13 @@ func TotalMediaCount(libs []LibraryData) int64 {
 	return total
 }
 
+// IsBookLibrary reports whether a library type participates in the
+// generic book surfaces (switcher, All Books, series). Podcasts are
+// feed-managed and surface via /podcasts only (plan §9/D13).
+func IsBookLibrary(typeName string) bool {
+	return typeName != "podcasts"
+}
+
 func uuidToString(id pgtype.UUID) string {
 	if !id.Valid {
 		return ""