fix: 根 files 改为子包运行时白名单，并删除过期提示词快照

整目录列入子包时，pi-subagents 上游 .npmignore 覆盖 .gitignore，导致
嵌套 node_modules（含第二套 Pi runtime）与 dist 被打包：64.9MB/19,570
文件降至 1.2MB/471 文件。新增 tests/package-files.test.ts 守护：无嵌套
node_modules/dist、扩展入口与 file: 依赖清单在包内、包内源码相对引用闭包。
同时删除无引用的 pi-default-system-prompt.md 旧快照（可用 /dump-system-prompt）。

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tests/web-search.test.ts

@@ -8,6 +8,9 @@ const packageJson = JSON.parse(await readFile(new URL("../package.json", import.
 	pi: { extensions: string[]; skills: string[] };
 };
 
+const filesIncludePackageDir = (files: string[], packageDir: string): boolean =>
+	files.some((entry) => entry === packageDir || entry.startsWith(`${packageDir}/`));
+
 test("pi-web-search is the single search surface and reads credentials from auth.json", () => {
 	const entries = packageJson.pi.extensions;
 	assert.ok(entries.includes("./pi-web-search/index.ts"), "the bundle must load pi-web-search");
@@ -27,7 +30,7 @@ test("pi-web-search is the single search surface and reads credentials from auth
 
 test("pi-web-search ships as a maintained file: dependency without upstream search packages", () => {
 	assert.equal(packageJson.dependencies["pi-web-search"], "file:./pi-web-search");
-	assert.ok(packageJson.files.includes("pi-web-search"));
+	assert.ok(filesIncludePackageDir(packageJson.files, "pi-web-search"));
 	assert.equal(packageJson.dependencies["@tavily/pi-extension"], undefined);
 	assert.equal(packageJson.dependencies["@keenable/pi-search"], undefined);
 	assert.equal(packageJson.dependencies["pi-mcp-adapter"], undefined, "Exa is a direct client now — no MCP adapter");