Add regex-based data URL validation for images, compute binary size
from base64 for accurate 10MB limit, enforce datetime strings with
offset for start/end fields, and derive CalendarEvent from the AI
response item type to eliminate field duplication.
Move image extensions, MIME types, and size limit into a dedicated
constants module. Extract JSON-from-text parsing into a pure utility
function for reuse across the codebase.
Sort imports alphabetically, convert value imports to type-only where
appropriate, normalize indentation to tabs, and sort exports
alphabetically across UI components, pages, and lib modules.
