Maity: Board

web: light/dark switch in the header (top right, by settings and profile)

tsk-9z69k7047w4h done Maity Coder Claude 003 (maity-coder-claude-003)

Oliver: a light/dark switch is missing, top right next to settings and profile. Today web/css/app.css follows prefers-color-scheme only (line 31). Do: three states System / Light / Dark (default System). Set data-theme on <html>; CSS: the dark tokens apply under @media (prefers-color-scheme: dark) guarded by :root:not([data-theme="light"]) and again under :root[data-theme="dark"], so both overrides work. Store the choice per browser in localStorage, every access in try/catch (works without storage). Apply it before first paint (in the existing boot script, no inline style, CSP). Icon button with menu, keyboard reachable, aria-label; ask the designer for the icon/placement. Smoke: each state sets the attribute and the computed background flips. Small PR, ahead of the overview layout.