[codex] Fix design-system review TOC overlay

[PerishCode]

Why

This PR fixes the narrow design-system review layout on top of #4260.

The pain being addressed is review usability: dense design-system contents need to remain scrollable in constrained layouts instead of being obscured by the table-of-contents overlay.

What users will see

In the #4260 design-system review flow, narrow layouts allow the contents area to scroll correctly instead of being blocked by the TOC overlay.

Surface area

• UI — design-system review layout in apps/web
• Keyboard shortcut — new or changed
• CLI / env var — new od subcommand or flag, new tools-dev / tools-pack / tools-pr flag, or new OD_* env var
• API / contract — new /api/* endpoint, new SSE event, or changed shape in packages/contracts
• Extension point — new entry under skills/, design-systems/, design-templates, or craft/, or change to the skills protocol
• i18n keys — added new translation keys (see TRANSLATIONS.md for the locale workflow)
• New top-level dependency — adding any new entry to the root package.json (dependencies or devDependencies); workspace-package package.json files are out of scope.
• Default behavior change — narrow review layout scrolling changes in the Agent-driven brand extraction + two-loop memory overhaul #4260 flow
• None — internal refactor, docs, tests, or translation update only

Screenshots

Not attached. Layout behavior is covered by the branch test.

Bug fix verification

Skipped. The branch includes focused layout test coverage, but I did not rerun it locally while opening this PR.

Validation

• Not run locally; PR opened from the existing branch for review.

[lefarcen]

🧪 This PR has changes that need a manual QA pass before merge — please hold off self-merging for now; we'll loop QA in once it's merge-ready (and design/product have signed off, where applicable).

[nettee]

@PerishCode I reviewed the narrow-layout TOC fix in apps/web/src/styles/design-system-flow.css and the matching coverage in apps/web/tests/styles/design-system-review-density.test.ts. The container-scoped override now drops the sticky TOC behavior in the single-column review layout while preserving the wide-layout rail assertions, and the targeted test additions line up with that change. I couldn't run the focused Vitest file in this reviewer worktree because node_modules are absent here, but the patch itself looks consistent and low-risk. Nice tight fix.

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