feat(reader): comic treatment for fixed-layout items in comics/manga libraries

PDFs shelved in comics or manga libraries (scanned manga, official manga
PDFs with text layers) now get comic reader treatment: bookmarks only —
no text-selection highlights, no annotations, no in-book search. Items
in ebooks libraries are completely unaffected, and EPUBs keep their
existing behavior everywhere.

- handlers: new exported ShouldTreatAsComic(libraryType, formatGroup) —
  true for fixed_layout/comic_archive in manga/comics libraries; the
  reader JSON API also exposes it as treat_as_comic
- router: the SSR reader page fetches the library type and passes
  TreatAsComic through ReaderMetadata into the init config
- reader: when treatAsComic is set, the PDF textLayer selection listener
  (mouse and touch paths) never attaches so no highlight popover can
  open; pointer mode is forced to pan (Smart/Text segment hidden);
  search button and toggleSearch are disabled; previously-created PDF
  highlights stop rendering
- bookmarks are unchanged (already page-index based for fixed layout),
  and device sync / OPDS / format classification are untouched since
  format_group stays fixed_layout

internal/router/reader.go

@@ -66,6 +66,13 @@ func registerReaderRoutes(cfg *Config) {
 		if !visible {
 			return renderErrorPage(c, "Access denied", "access_denied")
 		}
+		// Library type decides comic reader treatment: fixed-layout items
+		// (e.g. manga PDFs) shelved in comics/manga libraries are paged
+		// through like comics — bookmarks only, no highlights or search.
+		libraryWithType, err := cfg.Queries.GetLibraryWithType(c.Request().Context(), mediaItem.LibraryID)
+		if err != nil {
+			return renderErrorPage(c, "Failed to get library info", "library_error")
+		}
 		// Convert to template types. Reading state is deliberately NOT
 		// fetched or embedded: the reader pulls position, bookmarks, and
 		// annotations from the APIs at open time so the page can never
@@ -89,6 +96,7 @@ func registerReaderRoutes(cfg *Config) {
 			FileURL:          utils.ResolveMediaURL(mediaItem.LibraryID, pgtype.Text{String: mediaItem.FilePath, Valid: true}),
 			TotalCharacters:  mediaItem.TotalCharacters.Int64,
 			EstimatedPages:   sync.EstimatedPages(mediaItem.TotalCharacters.Int64),
+			TreatAsComic:     handlers.ShouldTreatAsComic(libraryWithType.TypeName, mediaItem.FormatGroup),
 		}
 		// Render template
 		var buf bytes.Buffer