Fix the existing Qt5 annotation app code for Andro...

Fix the existing Qt5 annotation app code for Android tablets (Android 5–9).

Focus only on the code:

• Fix all bugs, errors, crashes, freezes, and memory/resource issues.
• Improve performance, drawing/editing smoothness, responsiveness, and stability.
• Optimize CPU/RAM usage and prevent unnecessary allocations or UI blocking.
• Preserve all existing functionality and behavior.
• Make the code production-ready and robust on low-end Android tablets.

Do not add tests, explanations, comments, or documentation. Do not ask questions. Directly edit and return the updated files only.