.boards-result's one rule leaves src/web/style/content.ts and its name leaves docs/DESIGN.md §5d #4385

Replaces #4198. The class is used nowhere in the markup. Its only use left is the rule at src/web/style/content.ts:302 (.boards-result .table { margin-top: 12px; }).

Done:

• [ ] That rule is deleted, and .boards-result is removed from the style/content.ts bullet in docs/DESIGN.md §5d. git grep boards-result finds nothing.
• [ ] Run bun scripts/design-lint.ts --update. Commit docs/design/baseline.json only if the count goes down or stays equal.
• [ ] bun x tsc --noEmit and bun test test/design-lint.test.ts pass.
• [ ] Change nothing else. Earlier tries went red on tests this change does not touch. If the check fails on one, name it in the pull as unrelated rather than editing it.