Replace the header/status-bar layout with a full-height writing column
plus an always-visible side panel holding all metadata. Canonicalize the
new region vocabulary in CONTEXT.md (Writing column, Side panel) and retire
header / status line / edit area as terms-to-avoid.
Consequent sweeps: rewrite the Error UX section in side-panel terms and
give keyboard-disconnect a home (⌨ ✗, disconnect-only); drop the "line N"
readout; reconcile the render module ops and region shadow; sweep the
status-line/edit-area wording across the technical, roadmap, qfd, notes,
README, and ADR-003 docs (incl. the ~11→~13 line-count figure).
a848c05afa