Replace the accumulated per-widget decoration with short, documented
scales for type, weight, radius and motion. Fills are flat and elevation
is neutral, so accent colour marks state instead of decorating: the
gradients on buttons, pills, nodes and progress bars are gone, along with
the coloured glow shadows and the triple ring on the current unit.
Drop draw_node_halo() and the gradient aura on the learning path, which
painted the same bloom in the cairo layer.
Give the welcome page the app icon, a single-colour heading and an
unboxed paragraph. Restore keyboard focus rings, which were suppressed
everywhere, and clamp exercise bodies to a readable measure on wide
windows.
Fix two layout bugs found on the way: the statistics metric cards were
unequal because hexpand only shares leftover space, and a fraction of
zero still painted a stub of accent colour because GTK gives the progress
node a minimum width.
Co-authored-by: Cursor <cursoragent@cursor.com>
