~x-ai/grok-latest → B (3:2)

Side B fixes a real off-by-one bug: rank-history post indexes were 1-based with a silent unwrap_or(0) fallback, breaking links and disagreeing with 0-based /t/tag/N routes; it aligns RPC, garden HTML, types, and integration tests on the correct contract. Side A only deletes a leftover forum.rs duplicate and wires forum/ as the module root after a split—useful hygiene that removes ambiguity, but it adds no behavioral value beyond cleanup of already-split code.