[gmatossian]

Long nested Topic titles are hard to scan when roots, branches, and leaves have similar weight. Apply the accepted Quiet hierarchy design with a slightly wider sidebar, shallower indentation, clearer type weights, and a restrained current-row highlight. Compact three-column gaps preserve the existing dense-content width guarantee.

Closes #130.

Only the three sidebar presentation files and the corresponding visual-design documentation are included. JavaScript/RxJS topics and all other pending local changes remain separate.

Verification

• Formatting, lint, tool type checking, 57 app tests, and 146 tooling tests pass on this isolated revision.
• Production build passes with the existing nonfatal initial-bundle budget warning.
• 31 Chromium, WebKit, and real-catalog browser tests pass, including accessibility, dense-content width, repeated paths, and narrow navigation.
• Manual desktop, 320px, keyboard disclosure, navigation focus, and repeated current-occurrence checks pass.
• The complete local npm run check was attempted; Firefox stalled at browser startup after the other projects completed. A separate clean run of the three available browser projects passes. Full unmodified GitHub Actions, including Firefox, must pass before merge.

Review and acceptance

AI-assisted implementation, verification, and deliberate review of the complete four-file diff. No independent agent review was used for this bounded presentation change. Gabriel selected and approved the rendered design and explicitly delegated issue/PR delivery and merge after successful checks.