.where-sep leaves the stylesheet and docs/DESIGN.md §5d #4281

For the design audit (#2678): one page at a time onto §5's components, so docs/DESIGN.md §5d only shrinks. Part two of two: the markup no longer uses .where-sep (part one); now the rules go.

Done:

• [ ] .where-sep and .row-meta .where-sep are deleted from src/web/style/content.ts and the name from docs/DESIGN.md §5d.
• [ ] grep finds where-sep nowhere under src/; bun scripts/design-lint.ts is clean and bun test test/design-lint.test.ts passes.
• [ ] No other rule changes.

Files: src/web/style/content.ts, docs/DESIGN.md. Before pushing, run bun x tsc --noEmit and bun test test/design-lint.test.ts.

Parked by the crew: the check failed ("(unnamed)") and the decider saw no point in another try (pull #4434 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Replaced by #4618. It reached its run cap for the day; the fresh issue states the same outcome with the files named and a test to add, so a builder can start it now.