新增: 初始化 DevFlow 项目仓库

Tauri 2 + Vue 3 + Vite 6 桌面应用，Rust workspace 含 13 个 crate
(df-ai / df-storage / df-workflow / df-core / df-execute 等)。
核心能力：AI 聊天 agentic 循环(工具调用+人工审批)、工作流引擎、
任务/想法/项目/阶段管理、可追溯性，及配套前端组件。

Cargo.toml

@@ -0,0 +1,18 @@
+[workspace]
+members = [
+    "crates/*",
+    "src-tauri",
+]
+resolver = "2"
+
+[workspace.dependencies]
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+tokio = { version = "1", features = ["full"] }
+async-trait = "0.1"
+thiserror = "2"
+anyhow = "1"
+chrono = { version = "0.4", features = ["serde"] }
+uuid = { version = "1", features = ["v4"] }
+rusqlite = { version = "0.31", features = ["bundled"] }
+tracing = "0.1"