feat(variables): panel UX, variant-column color editing, theme presets, web mirror
#18 per-row management (resize edges, search with source indices, scroll
clamp, row overflow menu with delete+undo, inline hex cells), #19 variant-
column-targeted color/boolean writes (setValueForTheme parity, picker
seeds from the clicked column), #20 theme presets (.optheme io, app-level
persistence, shared preset menu), #21 full web host mirror (floating
panel replaces the read-only rail; keyboard/scroll/resize/blur routing).
Fixes the stale right-rail assertions in toolbar_panel_actions test.
Absorbs and completes the concurrent actor's variables-panel WIP.
14482a5d86