[codex] fix brief magazine layout overflow (#3921)

* fix(brief): keep magazine text within viewport

* fix(brief): address greptile feedback on magazine layout spec

- server/_shared/brief-render.js: fold overflow-wrap: anywhere into the
  existing standalone .digest h2 block instead of re-declaring the
  selector in the grouped rule (P2 readability fix).
- e2e/brief-magazine.spec.ts: track whether bounds selectors were
  actually found and assert presence before checking off-edge bounds, so
  a class rename or typo fails loudly instead of silently passing the
  trivially-true 0 ≥ -1 / 0 ≤ viewportWidth + 1 fallback (P2).