v4.0.0 — MCP tool surface consolidated to 53

• Breaking: MCP tool surface consolidated from 87 to 53 tools (17 core + 36 advanced); tool families merged into mode/action hubs, no transitional aliases — migration guide: docs/migration-v4.md
• Breaking: legacy Playbook scope migration moved out of MCP into the owner-only local CLI (engram playbook scope ...)
• Hardening: review_staging now runs the write gate for every action including list; merged tools keep the strictest gate of their family

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• 破坏性：MCP 工具面从 87 合并为 53（17 核心 + 36 高级），操作族合并为 mode/action 中枢工具，不设过渡别名——迁移指南：docs/migration-v4.zh-CN.md
• 破坏性：旧 Playbook 作用域迁移移出 MCP，改为 owner 专用本地 CLI（engram playbook scope ...）
• 加固：review_staging 对包括 list 在内的所有操作先过写入门；合并工具取所属族最严门