Drop hub cold-start announce fan-out (nothing consumes it, wakes every eng-aro member on each bounce)

Elazar 2026-07-13: 'stop dming all agents in aro:' — the hub cold-start announce (hub.mjs:5930-5942) fans one 'hub cold start: vX island=main' announce per aro:llmmsg-srv-engineering member on EVERY boot, waking bin-venus-cc/coder-chatduo-cc/nw-lezama-cc/pm-llmmsgsrv-cc for a fact none acts on. Verified ZERO consumers: grep across hub/bridge/chat-duo-web/~/.local/bin finds nothing reading the 'hub cold start' body or the coldstart tag. FIX: remove the per-member insert loop (lines 5935-5941, the stmtInsertMsg fan) so no cold-start DM is emitted. KEEP: the console.log boot lines (real record) + stmtRegister/stmtPin of the synthetic llmmsg-srv-hub agent (needed by other hub-sender paths, unrelated to the announce). Same family + rationale as VENUS-232 (dropped the silence-kick member-broadcast). Small, surgical, docs-verifiable no-consumer.