chore: 初始化 BlockFlow Workbench 仓库

建立前端与 Tauri 桌面端的首个版本提交，包含核心编辑器、项目文件读写、测试与构建配置。

补充 Git 忽略规则和换行规范，排除依赖、构建产物、本地运行日志与临时验证文件，方便在其他电脑继续开发。

src/editor/extensions/LoopBlockExtension.ts

@@ -0,0 +1,43 @@
+import { mergeAttributes, Node } from "@tiptap/core"
+
+export const LoopBlockExtension = Node.create({
+  name: "loopBlock",
+  group: "block",
+  content: "block+",
+  defining: true,
+  isolating: true,
+
+  addAttributes() {
+    return {
+      id: { default: null },
+      source: { default: "items" },
+      itemName: { default: "item" },
+      indexName: { default: "" }
+    }
+  },
+
+  parseHTML() {
+    return [{ tag: "section[data-blockflow-loop]" }]
+  },
+
+  renderHTML({ HTMLAttributes, node }) {
+    const suffix = node.attrs.indexName ? ` index ${node.attrs.indexName}` : ""
+    return [
+      "section",
+      mergeAttributes(HTMLAttributes, {
+        "data-blockflow-loop": "",
+        "data-block-id": node.attrs.id,
+        "data-source": node.attrs.source,
+        "data-item-name": node.attrs.itemName,
+        "data-index-name": node.attrs.indexName,
+        class: "bf-structured-block"
+      }),
+      [
+        "div",
+        { class: "bf-block-heading bf-loop-heading", contenteditable: "false" },
+        `▾ for ${node.attrs.itemName} in ${node.attrs.source}${suffix}`
+      ],
+      ["div", { class: "bf-block-content" }, 0]
+    ]
+  }
+})