xAI adds memory to Grok Build

Added memory to Grok Build — at the end of each turn, it skims the work in the background and writes down the team's coding conventions, the reasons behind decisions and facts about project infrastructure in topic-specific Markdown files (testing.md, code-style.md, etc.), then reads the relevant topics first when starting related work. Workspace scope and global scope are kept separate; `/memory` opens it for viewing, and `/dream` organizes recent notes by topic. It does not record task state, tentative conclusions, secrets or anything already in the repository or docs, and instructions in the current conversation take priority over memory.