fix(douyin): narrow getDraftCommand return type to fix TS2722 build failure

[jackwener]

Summary

• Fix tsc --noEmit build failure introduced by fix(douyin): repair creator draft flow #640's draft test refactoring
• getDraftCommand() returns CliCommand where func is optional, causing TS2722 at every cmd.func(...) call site
• Add type narrowing assertion: cmd as typeof cmd & { func: NonNullable<typeof cmd.func> } so TypeScript knows func is defined after the runtime guard

Test plan

• npx tsc --noEmit passes (no draft.test.ts errors)
• npx vitest run src/clis/douyin/draft.test.ts --project adapter — 10/10 pass