This Pull Request fixes the book upload dialog box's lack of visual feedback during the file ingestion process.
### Key Changes:
1. **Interactive `ingesting-state` Loading State**: Added a dedicated, beautiful neon-green loader that displays `Saving book to library...` with a pulsing neon spinner while the HTTP POST upload request is in flight. This cleanly replaces the form during ingestion, preventing users from clicking disabled/unresponsive inputs or submitting twice.
2. **Premium Glowing Button Loader**: Updated `.btn-loading` styling in `BookIngestionModal.razor.css` to use a high-contrast white-and-neon-green glowing spinner (`border-top-color: var(--nexus-neon)`) instead of an invisible black `#000` spinner on a faded, disabled dark button.
3. **Build & Test Verified**: Successfully verified that the entire solution compiles cleanly with 0 compilation errors (`dotnet build`) and that all unit/integration tests continue to pass perfectly (`dotnet test`).
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Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #66
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>