feat(ts): centralized library storage with cookie-based SSR support

- storage.ts: Centralize ALL_LIBRARIES = "__all__" sentinel constant.
  setSelectedLibrary() now writes both localStorage and a cookie
  (selectedLibrary, Path=/, SameSite=Lax, max-age=365d). The
  sentinel "__all__" is used in both storage mediums — empty strings
  are never stored. getSelectedLibrary() maps __all__ back to "".
  Cookie enables server-side rendering to read the stored library
  selection without access to localStorage.

- library-switcher.ts: Import ALL_LIBRARIES and setSelectedLibrary/
  getSelectedLibrary from storage.ts instead of managing localStorage
  directly. Remove local constants.

- dashboard.ts: Remove duplicate localStorage.setItem call that was
  overwriting the __all__ sentinel with raw empty string. Fix
  reloadPage() and scan-complete handler to work with empty libraryId.
  openDashboardSettings/saveDashboardSettings show clear messages for
  All Libraries mode.

- collections.ts: Remove library switcher initialization from the
  collections list page — the list page no longer has a switcher.

- series.ts: Rewrite to use initLibrarySwitcher from library-switcher
  module and switchWithTransition for navigation. Series card links
  no longer include library_id in their URLs.

- bookshelf.ts: Autocomplete fetch calls handle empty libraryId
  correctly for All Libraries mode.

- search.ts, collection-rules.ts: Use setSelectedLibrary() and
  getSelectedLibrary() from storage.ts instead of direct localStorage
  access.

web/src/search.ts

@@ -1,4 +1,5 @@
 import { Alpine } from "./alpine";
+import { setSelectedLibrary } from "./storage";
 
 let searchInputTimeout: ReturnType<typeof setTimeout> | null = null;
 const SEARCH_DEBOUNCE_MS = 300;
@@ -298,7 +299,7 @@ function searchEscapeHtml(text: string): string {
 }
 
 function selectLibraryAndBook(libraryId: string, bookId: string): void {
-  localStorage.setItem("selectedLibrary", libraryId);
+  setSelectedLibrary(libraryId);
   localStorage.setItem("selectedBook", bookId);
   hideSearchResults();
 }