content-card used `overflow-scroll`, which renders scrollbar tracks even
when the content fits — visible as superfluous bars around the admin chart
cards. Switch to `overflow-auto` so scrollbars only appear when content
genuinely overflows (e.g. wide data tables still scroll).
Also add a gitignored ./tmp/ scratch directory (tracked via .gitkeep) and
document in AGENTS.md that temp files belong there.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
