Course 0: t27 basics in 27 modules with infographics

Add course 0, t27-basics, before the FPGA course and the AI numbers course: 27 modules of one lesson on the t27 language, each with its own widget and a lesson spec that compiles in the browser, chained 0 -> 1 -> 2 in specs/course/courses.t27, with a Russian bundle and a blog post in English and Russian. Built by the course-27 skill steps.