Pie chart shows expense breakdown by category with color-coded slices.
Bar chart shows income vs expense for the last 6 months. Line chart
shows cumulative daily net trend. All charts render via plotters
BitMapBackend to GDK MemoryTexture for display. Month navigation
shared across all three charts.
Initialize SQLite database at XDG data directory on app startup.
Categories now load from database with emoji icons. Save button
validates input, inserts transaction, shows toast notification,
clears the form, and refreshes the recent transactions list.
