- Drop border-bottom lines between header / title / tags / toolbar
so they read as one continuous input surface.
- Add a single border-top above the editor body so the body's
existing boundary stays clear.
- Notes rail gets --color-bg-card so it no longer visually merges
with the tasks panel (both previously shared --color-surface).
Dropped the rail's border-right since the tint now carries the
division from the editor pane.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>