Per Ryan — category drill-down already shows newest-first ordering so
the standalone Recent Threads list was redundant. Each category card now
shows "Last post: <title> · <relative time>" below the description so
glanceable activity stays on the landing page. Categories API joins one
latest thread per category in a single round-trip (in_ + limit + group
in memory) instead of N+1.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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