Atlas & Prometheus agents can write to Vello memory again

The six GTM (Atlas) and PRODUCT (Prometheus) agent workflows were wiring the Vello MCP server through an mcp_config: input that claude-code-action@v1 does not accept — it was silently dropped, so the mcp__vello__* tools never loaded and those agents couldn't search or store memory at all. They now write the MCP config to a file and pass it via --mcp-config, matching the pattern the core build/review/QA/respond/rework workflows already use. No user-facing UI change; the GTM and PRODUCT agents now actually participate in Vello memory as intended.