feat(typescript): add core infrastructure modules

- Add centralized API type definitions (types/api.d.ts)
  - Interfaces for all API responses matching Go handler JSON
  - Snake_case field names matching actual API responses
  - Source file references in comments for verification

- Add API client module (api.ts)
  - Procedural get/post/put/delete functions
  - Automatic auth header injection
  - Exported to window for cross-module access

- Add DOM utilities (dom.ts)
  - escapeHtml for safe HTML rendering
  - querySelector wrappers with null checks
  - Element creation helpers

- Add event delegation helpers (events.ts)
  - Reusable event delegation pattern
  - Data attribute selectors for dynamic content

- Add localStorage wrapper (storage.ts)
  - Type-safe token management
  - Theme persistence helpers

web/src/storage.ts

@@ -0,0 +1,83 @@
+function getToken(): string | null {
+    return localStorage.getItem('token');
+}
+
+function setToken(token: string): void {
+    localStorage.setItem('token', token);
+}
+
+function removeToken(): void {
+    localStorage.removeItem('token');
+}
+
+function getRefreshToken(): string | null {
+    return localStorage.getItem('refresh_token');
+}
+
+function setRefreshToken(token: string): void {
+    localStorage.setItem('refresh_token', token);
+}
+
+function removeRefreshToken(): void {
+    localStorage.removeItem('refresh_token');
+}
+
+function getTheme(): string {
+    return localStorage.getItem('theme') || 'tokyo-night';
+}
+
+function setTheme(theme: string): void {
+    localStorage.setItem('theme', theme);
+}
+
+function getSelectedLibrary(): string | null {
+    return localStorage.getItem('selectedLibrary');
+}
+
+function setSelectedLibrary(libraryId: string): void {
+    localStorage.setItem('selectedLibrary', libraryId);
+}
+
+function getSelectedBook(): string | null {
+    return localStorage.getItem('selectedBook');
+}
+
+function setSelectedBook(bookId: string): void {
+    localStorage.setItem('selectedBook', bookId);
+}
+
+function clearAll(): void {
+    localStorage.clear();
+}
+
+(window as any).storage = {
+    getToken,
+    setToken,
+    removeToken,
+    getRefreshToken,
+    setRefreshToken,
+    removeRefreshToken,
+    getTheme,
+    setTheme,
+    getSelectedLibrary,
+    setSelectedLibrary,
+    getSelectedBook,
+    setSelectedBook,
+    clearAll
+};
+
+export {
+    getToken,
+    setToken,
+    removeToken,
+    getRefreshToken,
+    setRefreshToken,
+    removeRefreshToken,
+    getTheme,
+    setTheme,
+    getSelectedLibrary,
+    setSelectedLibrary,
+    getSelectedBook,
+    setSelectedBook,
+    clearAll
+};