feat(backend): add domain store, learning services, and seed data

Persist LMS entities and implement hearts/watch rules plus curriculum bootstrap.

backend/internal/store/learning_test.go

@@ -0,0 +1,36 @@
+package store_test
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"pargar/backend/internal/db"
+	"pargar/backend/internal/store"
+)
+
+func TestLearningOverviewSmoke(t *testing.T) {
+	dsn := os.Getenv("DATABASE_URL")
+	if dsn == "" {
+		dsn = "postgres://pargar:f479ad70f076f25594b73b767691be4b295901c4430ed208@localhost:5432/pargar?sslmode=disable"
+	}
+	ctx := context.Background()
+	pool, err := db.Connect(ctx, dsn)
+	if err != nil {
+		t.Skip("postgres unavailable:", err)
+	}
+	defer pool.Close()
+	st := store.New(pool)
+	o, err := st.LearningOverview(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if o == nil {
+		t.Fatal("nil overview")
+	}
+	students, err := st.ListStudentLearning(ctx, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = students
+}