Lab editing and group grades

- academic-service: PUT /labs/{id} (title, deadline, defense, points, status,
  description), POST/PUT/DELETE variants endpoints
- progress-service: lab_grades table, POST/GET /api/v1/grades, GET /me/grades
- gateway: routes for /api/v1/assign and /api/v1/grades
- web: lab edit page (metadata + per-variant forms + add/delete variant)
- web: group page shows grades matrix per lab with editable score inputs
  and computed average column
- web: student dashboard renders statement via markdown, shows deadline

services/progress-service/src/main/resources/db/migration/V3__grades.sql

@@ -0,0 +1,9 @@
+-- Lab grades: one grade per student per lab.
+
+CREATE TABLE lab_grades (
+    student_id uuid        NOT NULL,
+    lab_id     uuid        NOT NULL,
+    score      numeric(4,1) NOT NULL,
+    updated_at timestamptz NOT NULL DEFAULT now(),
+    PRIMARY KEY (student_id, lab_id)
+);