refactor(bookshelf): migrate from DOM manipulation to Alpine.js reactive state

Replace direct DOM manipulation with Alpine.js reactive state variables:
- Add isLoading and hasBooks state to bookshelf component
- Convert loadBookshelf() to update isLoading state instead of toggling DOM visibility
- Convert renderBookshelf() to use reactive state for empty state handling
- Remove redundant getElementById() calls for loading/empty-state elements

This change improves maintainability by:
- Centralizing UI state in the Alpine component
- Eliminating direct DOM manipulation scattered across functions
- Making the component's state more explicit and trackable
- Following Alpine.js reactive programming patterns

The UI will now respond to state changes automatically rather than requiring
manual DOM updates throughout the lifecycle methods.

web/src/bookshelf.ts

@@ -33,13 +33,7 @@ async function loadBookshelf(libraryId: string): Promise<void> {
   const token = localStorage.getItem("token");
   if (!token || !libraryId) return;
 
-  const loading = document.getElementById("loading");
+  this.isLoading = true;
-  const booksGrid = document.getElementById("books-grid");
-  const emptyState = document.getElementById("empty-state");
-
-  if (loading) loading.style.display = "block";
-  if (booksGrid) booksGrid.classList.add("hidden");
-  if (emptyState) emptyState.classList.add("hidden");
 
   try {
     const response = await fetch(
@@ -60,8 +54,7 @@ async function loadBookshelf(libraryId: string): Promise<void> {
   } catch (error) {
     console.error("Error loading bookshelf:", error);
     showToast("Error loading books", "error");
-  } finally {
+    this.isLoading = false;
-    if (loading) loading.style.display = "none";
   }
 }
 
@@ -76,21 +69,14 @@ function showEmptyState(): void {
 }
 
 function renderBookshelf(): void {
-  const booksGrid = document.getElementById("books-grid");
-  const emptyState = document.getElementById("empty-state");
-  const loading = document.getElementById("loading");
-
-  if (!booksGrid) return;
-
-  if (loading) loading.style.display = "none";
-  if (emptyState) emptyState.classList.add("hidden");
-
   if (!mediaItems || mediaItems.length === 0) {
-    showEmptyState();
+    this.isLoading = false;
+    this.hasBooks = false;
     return;
   }
 
-  booksGrid.classList.remove("hidden");
+  const booksGrid = document.getElementById("books-grid");
+  if (!booksGrid) return;
 
   const booksPerShelf = 6;
   const shelves: unknown[][] = [];
@@ -199,6 +185,11 @@ export {
 };
 
 Alpine.data("bookshelf", () => ({
+  // State Variables
+  isLoading: true,
+  hasBooks: false,
+
+  // Methods
   changePage,
   initBookshelf,
   loadBookshelf,