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/library-switcher.ts

@@ -1,10 +1,9 @@
 import { Alpine } from "./alpine";
+import { ALL_LIBRARIES, getSelectedLibrary, setSelectedLibrary } from "./storage";
 import { showToast } from "./toast";
 
-const STORAGE_KEY = "selectedLibrary";
-
 export function getCurrentLibraryId(): string {
-  return localStorage.getItem(STORAGE_KEY) || "";
+  return getSelectedLibrary();
 }
 
 export async function switchWithTransition(
@@ -60,8 +59,10 @@ export function initLibrarySwitcher(options: LibrarySwitcherOptions): void {
   ) as HTMLSelectElement;
   if (!librarySelect) return;
 
-  const stored = localStorage.getItem(STORAGE_KEY);
-  if (stored) {
+  const stored = localStorage.getItem("selectedLibrary");
+  if (stored === ALL_LIBRARIES) {
+    librarySelect.value = "";
+  } else if (stored) {
     const option = librarySelect.querySelector(
       `option[value="${stored}"]`,
     );
@@ -72,10 +73,9 @@ export function initLibrarySwitcher(options: LibrarySwitcherOptions): void {
 
   librarySelect.addEventListener("change", async (e) => {
     const target = e.target as HTMLSelectElement;
-    if (!target.value && target.value !== "") return;
-
     const libraryId = target.value;
-    localStorage.setItem(STORAGE_KEY, libraryId);
+
+    setSelectedLibrary(libraryId);
     await options.onSwitch(libraryId);
   });
 }