feat: add command pack protocol and plugin management

- define the Command Pack API and integrate pack loading into the CLI runtime
- add product-specific package, command prefix, and credential access policies
- add plugin install, link, list, and remove commands
- add validation, tests, documentation, and generated command references

packages/kscli/tests/e2e/command-packs.e2e.test.ts

@@ -0,0 +1,14 @@
+import { describe, expect, test } from "vite-plus/test";
+import { runKscli } from "./helpers.ts";
+
+describe("e2e: kscli Command Pack host", () => {
+  test("keeps the shared host inactive with the default empty policy", async () => {
+    const help = await runKscli(["--help"]);
+    expect(help.exitCode, help.stderr).toBe(0);
+    expect(help.stderr).not.toContain("plugin install");
+
+    const result = await runKscli(["plugin", "list"]);
+    expect(result.exitCode).not.toBe(0);
+    expect(result.stderr).toMatch(/Unknown command/i);
+  });
+});