feat: add slash command help

hub/test/unit/slash-commands.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from "vitest";
+import { parseSlashHelpSubcommand, parseSlashInvocation } from "../../src/feishu/slashCommands.js";
+
+describe("slash command parser", () => {
+  it("parses a slash invocation without resolving it", () => {
+    expect(parseSlashInvocation("/new")).toEqual({ name: "new", args: [] });
+    expect(parseSlashInvocation("/review 看看这节")).toEqual({ name: "review", args: ["看看这节"] });
+    expect(parseSlashInvocation("写教案")).toBeNull();
+  });
+
+  it("parses help subcommands only in the exact /<command> help form", () => {
+    expect(parseSlashHelpSubcommand({ name: "new", args: ["help"] })).toBe("new");
+    expect(parseSlashHelpSubcommand({ name: "unknown", args: ["help"] })).toBe("unknown");
+    expect(parseSlashHelpSubcommand({ name: "new", args: ["help", "please"] })).toBeNull();
+    expect(parseSlashHelpSubcommand({ name: "help", args: ["new"] })).toBeNull();
+  });
+});