Kairo: RSVP Reader

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- Added support for PDF, DOCX, FB2, PRC, AZW, TXT, Markdown, and HTML books.
- Improved automatic file-format detection for more reliable imports.
- Made selectable-text PDF imports faster and more dependable.
- Added clearer guidance about supported formats and import requirements.
- Added in-app notifications when a new Play Store update is available.
- Improved Android compatibility, performance, and overall stability.