docs: add css/html cleanup todo note

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/css-html-cleanup-todo.md

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+# CSS / HTML cleanup — loose ends
+
+Found during sidebar/TOC refactor session (2026-04-11).
+
+## Redundant resets
+
+- `nav[data-nav="sidebar"] ul li { margin: 0; padding: 0 }` — browser default for `<li>` already has no margin/padding. No-op, remove.
+- `aside[data-toc] nav ul li { margin: 0; padding: 0 }` — same.
+
+## Semantic HTML
+
+- `<small>← Previous</small>` and `<small>Next →</small>` in prev/next footer (`docs/single.html`, `vault/single.html`) — `<small>` is fine print, not a directional label. Replace with something appropriate.
+- `role="main"` on `<article>` in `docs/single.html` — redundant and misleading. `<article>` does not map to the `main` landmark; `<main>` does. Remove the attribute.
+
+## i18n
+
+- `"On this page"` is hardcoded in `docs/single.html` and `vault/single.html`. Move to Hugo i18n strings or a site param before adding any second language.