Part of #617.

What to build

modules/State.lua and modules/Render.lua.

State lives in <workspace>/.progress/State.json, written with import("core.base.json"): per exercise {attempts, hintsUsed, secondsSpent, completedAt}, plus current and a day streak. It must survive restarts and never be required for the checker to work.

Terminal rendering only, no HTML, no colours that break on a plain terminal:

Ch0 Setup            ###### 2/2  done
Ch1 The C++ you need ##....  1/4
Ch2 The first loop   ......  0/4
Ch3 Systems          ......  0/4
                     ----------------
                     3/14   streak 2 days
next: 01-02 a function that takes a reference

Done when

• xmake learn --list shows every exercise as done, current or locked
• xmake learn --progress renders the bars, totals, streak and next exercise
• state survives a restart and a curriculum update
• --json exposes the same data for tooling

Depends on

#621