v0.19.0 - Quiz and assignment follow-ups

Highlights

• Staff can fix an answer key after students have started: saving the questions regrades every submitted attempt, keeps points a reviewer set by hand, and records a regrade per attempt in the audit log (Spec 12).
• A quiz can limit each attempt to a number of minutes inside its window; the countdown shows the attempt's own deadline and the server submits the attempt when it passes.
• An assignment can accept late submissions until a second date with a flat percentage penalty; late work is marked, the raw grade stays on the submission and the penalised score goes to the gradebook, and students see both once released.
• The API server bounds how long a client may take to send a request (UNICOURSE_READ_TIMEOUT, default 30 s) while uploads get their own longer deadline (UNICOURSE_UPLOAD_TIMEOUT, default 10 min); a timed-out read is logged as 499.
• Three new end-to-end cases cover the time limit, the regrade and the late penalty.

What's Changed

Changes

• P19-L6: server read timeouts (UNICOURSE_READ_TIMEOUT, UNICOURSE_UPLOAD_TIMEOUT), 499 on a timed-out read by @kapildev333 in #176
• P19-L2: migration 0011, assessment time limit / late window / penalty fields, effective-deadline SQL, timed-quiz questions gate by @kapildev333 in #179
• P19-L5: late submissions with a penalty (late window, late flag, penalised gradebook score) by @kapildev333 in #180
• P19-L4: per-attempt time limit (effective deadline on save, submit and the sweeper; Attempt.deadlineAt) by @kapildev333 in #181
• P19-L3: regrade submitted attempts after an answer-key change (ids on questions, manual marks kept and capped) by @kapildev333 in #183
• P19-L7: web for Spec 12 - time limit, regrade editor mode, late submissions with penalty by @kapildev333 in #184
• P19-L8: e2e E-QUIZ-11 (time limit), E-QUIZ-12 (regrade), E-ASG-09 (late penalty) by @kapildev333 in #186

Full Changelog: v0.18.0...v0.19.0