新增: MCP Server(df-mcp crate + stdio 协议 + CLI 子命令)

依据 F-260619-02 设计,对外暴露数据层接入 Claude Code/Cursor:
- 新建 df-mcp crate:JSON-RPC 2.0 over stdio(initialize/tools/list/tools/call)
- 暴露 19 数据层工具(项目/任务/灵感/工作流/回收站),复用 df-storage Repo 零重复 CRUD
- 三层安全降级:High 风险(delete/purge/run_workflow)tools/list 不暴露+dispatch 拒+handler 二次拒;Medium 允许+审计日志;--read-only 仅 Low
- 不暴露文件系统工具(防绕过应用内路径校验)
- Tauri CLI 子命令 devflow mcp-server [--db/--read-only/--print-config]
- SQLite WAL 已启用(复用 Database::open),应用与 MCP server 并发写安全

自验: df-mcp 8 passed + workspace EXIT 0

Cargo.lock

@@ -773,6 +773,7 @@ dependencies = [
  "df-ai",
  "df-execute",
  "df-ideas",
+ "df-mcp",
  "df-nodes",
  "df-project",
  "df-storage",
@@ -848,6 +849,21 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "df-mcp"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "df-storage",
+ "df-types",
+ "futures",
+ "serde",
+ "serde_json",
+ "tokio",
+ "tracing",
+ "uuid",
+]
+
 [[package]]
 name = "df-nodes"
 version = "0.1.0"