fix: 修复构建脚本跨平台 import specifier 路径规范化

- toImportSpecifier() 使用 replaceAll 替代 split(sep).join，明确 ESM import specifier 语义
- 增加 relativePath 可选参数支持测试注入 Windows relative 语义
- 重写 Windows 路径测试，使用 node:path.win32 显式模拟而非依赖当前平台 sep
- 更新 DEVELOPMENT.md 记录构建 code generation 约定
- 同步 static-asset-embedding 和 windows-test-compat spec 新增要求

scripts/build-common.ts

@@ -1,5 +1,5 @@
 import { readdir, rm, writeFile } from "node:fs/promises";
-import { join, relative, sep } from "node:path";
+import { join, relative } from "node:path";
 import { fileURLToPath } from "node:url";
 
 import { validateVersion } from "./bump-version-logic";
@@ -104,8 +104,12 @@ export async function scanDir(dir: string, prefix: string): Promise<string[]> {
   return paths;
 }
 
-export function toImportSpecifier(fromDir: string, targetPath: string) {
-  return relative(fromDir, targetPath).split(sep).join("/");
+export function toImportSpecifier(
+  fromDir: string,
+  targetPath: string,
+  relativePath: (from: string, to: string) => string = relative,
+) {
+  return relativePath(fromDir, targetPath).replaceAll("\\", "/");
 }
 
 export async function viteBuild() {