Shared

Shared base for the excalidrawer diagram skills (flowchart / timeline / architecture / sequence / comparison). Holds the cross-cutting conventions every type skill depends on — MCP precheck + CLI fallback, sugar schema reference, color palette, output file naming, label language, export format selection, and iteration rules. The type skills declare "前置条件：先 Read ../shared/SKILL.md" and rely on this. Not a standalone drawing skill — read it first, then follow the type-specific recipe. 通用约定 / 基座 / sugar / 配色 / 命名 / 导出格式。