feat: add book info modal to admin pending approval cards

Adds an info icon button (top-right of each card) in the Requests
Awaiting Approval section. Clicking it opens AudiobookDetailsModal
with full book details (cover, description, narrator, series, genres,
etc.) and embeds the Approve / Search / Deny action buttons so admins
can review and act without navigating away from the admin panel.

Implementation:
- AudiobookDetailsModal: adds optional `adminActions` prop rendered as
  a second row inside the existing sticky action bar
- admin/page.tsx: adds detailsAsin/detailsRequestId state, info button
  per card (conditional on audibleAsin presence), and AudiobookDetailsModal
  wired with admin action buttons matching the card button behaviour
- Documentation updated: request-approval.md, components.md, TABLEOFCONTENTS.md

Closes #157

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

documentation/admin-features/request-approval.md

@@ -259,8 +259,11 @@ Update user (includes autoApproveRequests field)
   - Title and author
   - User avatar and username
   - Request timestamp (relative: "2 hours ago")
+  - Info button (ⓘ, top-right corner) — opens AudiobookDetailsModal for full book details
   - Approve button (green, checkmark icon)
+  - Search button (blue, magnifier icon) — opens InteractiveTorrentSearchModal
   - Deny button (red, X icon)
+- **Info modal:** `AudiobookDetailsModal` rendered with `adminActions` prop containing Approve/Search/Deny buttons, allowing admin to review full book details (cover, description, series, genres, narrator, etc.) without leaving the approval workflow
 - Auto-refreshes every 10 seconds (SWR)
 - Loading states on buttons during approval/denial
 - Success/error toast notifications