feat: add library management with Calibre support

[OGKevin]

Implement a trait-based library abstraction layer that enables reading
book metadata from Calibre databases. Add unified error handling and
Tauri commands for library operations.

• Create BookLibrary trait for extensible library backend support
• Implement CalibreLibrary with thread-safe database access
• Add AppError enum for consistent error handling across modules
• Implement LibraryState for managing open library instances
• Add Tauri commands: library_open, library_get_all_books,
  library_get_book, library_get_book_count
• Add comprehensive tests for library operations and error cases
• Organize imports alphabetically across modules (style)

Change-Id: 4050ec25b8f88b0eb211f6691a725e6d
Change-Id-Short: vzuzlnxuorkr

[OGKevin]

@copilot Can you have a look at the failing CI.

• The code must be linted and the violations fixed.
• I believe the frontend test might have a race condition

- useLibrary " can manually load books after opening library

    expect(jest.fn()).toHaveBeenCalledTimes(expected)

    Expected number of calls: 1
    Received number of calls: 2

      258 |     });
      259 |
    > 260 |     expect(libraryApi.libraryGetAllBooks).toHaveBeenCalledTimes(1);
          |                                           ^
      261 |   });
      262 |
      263 |   describe("Bug fix: Backend calls should be made when opening library with known path", () => {

      at Object.toHaveBeenCalledTimes (src/__tests__/hooks/useLibrary.test.tsx:260:43)

As this test passes locally. Investigate if this is possible and attempt to address it.

• flake.nix needs to be updated with new hashes for cargo and pnpm, as the dependency changed.

Make a separate commit for each bullet point.

[Copilot]

@OGKevin I've opened a new pull request, #62, to work on those changes. Once the pull request is ready, I'll request review from you.