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

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

backend/internal/service/hearts_staff_test.go

@@ -0,0 +1,28 @@
+package service
+
+import (
+	"context"
+	"testing"
+
+	"pargar/backend/internal/models"
+)
+
+func TestConsumeHeartsSkipsStaff(t *testing.T) {
+	h := &HeartsService{}
+	for _, role := range []models.Role{models.RoleAdmin, models.RoleMentor} {
+		u := &models.User{ID: 1, Role: role, Hearts: 1, IsLocked: false}
+		out, lost, err := h.ConsumeHearts(context.Background(), u, 3)
+		if err != nil {
+			t.Fatalf("%s: unexpected err %v", role, err)
+		}
+		if lost != 0 {
+			t.Fatalf("%s: expected 0 hearts lost, got %d", role, lost)
+		}
+		if out.Hearts != 1 {
+			t.Fatalf("%s: hearts should stay 1, got %d", role, out.Hearts)
+		}
+		if out.IsLocked {
+			t.Fatalf("%s: staff must not lock", role)
+		}
+	}
+}