.bt-bar, .bt-grid, .bt-group, .bt-hist, .bt-name, .bt-procs, .bt-row, .bt-val leave the stylesheet and docs/DESIGN.md §5d #4167

Part two of #3866. It starts once part one has removed these names from the markup.

Done:

• [ ] git grep each of .bt-bar .bt-grid .bt-group .bt-hist .bt-name .bt-procs .bt-row .bt-val: no use is left in src/ but its rule. If one is still used somewhere, keep it and say where in the pull.
• [ ] The rules leave src/web/style/content.ts (and any reduced-motion block), and the names leave their §5d bullet in docs/DESIGN.md.
• [ ] Run bun scripts/design-lint.ts --update and commit docs/design/baseline.json only if the count goes down or stays equal. bun test test/design-lint.test.ts passes.

Files: src/web/style/content.ts, docs/DESIGN.md, docs/design/baseline.json. Before pushing: bun x tsc --noEmit and bun test test/design-lint.test.ts. Rebase right before pushing: DESIGN.md changes under everyone.

Parked by the crew: the check failed ("(unnamed)") and the decider saw no point in another try (pull #4346 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Replaced by #4616. 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.