feat(announcements): add admin/user announcement system

Implements announcements end-to-end (admin CRUD + read status, user list + mark read) with OR-of-AND targeting. Also breaks the ent<->service import cycle by moving schema-facing constants/targeting into a new domain package.

backend/internal/service/announcement_targeting_test.go

@@ -0,0 +1,67 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAnnouncementTargeting_Matches_EmptyMatchesAll(t *testing.T) {
+	var targeting AnnouncementTargeting
+	require.True(t, targeting.Matches(0, nil))
+	require.True(t, targeting.Matches(123.45, map[int64]struct{}{1: {}}))
+}
+
+func TestAnnouncementTargeting_NormalizeAndValidate_RejectsEmptyGroup(t *testing.T) {
+	targeting := AnnouncementTargeting{
+		AnyOf: []AnnouncementConditionGroup{
+			{AllOf: nil},
+		},
+	}
+	_, err := targeting.NormalizeAndValidate()
+	require.Error(t, err)
+	require.ErrorIs(t, err, ErrAnnouncementInvalidTarget)
+}
+
+func TestAnnouncementTargeting_NormalizeAndValidate_RejectsInvalidCondition(t *testing.T) {
+	targeting := AnnouncementTargeting{
+		AnyOf: []AnnouncementConditionGroup{
+			{
+				AllOf: []AnnouncementCondition{
+					{Type: "balance", Operator: "between", Value: 10},
+				},
+			},
+		},
+	}
+	_, err := targeting.NormalizeAndValidate()
+	require.Error(t, err)
+	require.ErrorIs(t, err, ErrAnnouncementInvalidTarget)
+}
+
+func TestAnnouncementTargeting_Matches_AndOrSemantics(t *testing.T) {
+	targeting := AnnouncementTargeting{
+		AnyOf: []AnnouncementConditionGroup{
+			{
+				AllOf: []AnnouncementCondition{
+					{Type: AnnouncementConditionTypeBalance, Operator: AnnouncementOperatorGTE, Value: 100},
+					{Type: AnnouncementConditionTypeSubscription, Operator: AnnouncementOperatorIn, GroupIDs: []int64{10}},
+				},
+			},
+			{
+				AllOf: []AnnouncementCondition{
+					{Type: AnnouncementConditionTypeBalance, Operator: AnnouncementOperatorLT, Value: 5},
+				},
+			},
+		},
+	}
+
+	// 命中第 2 组（balance < 5）
+	require.True(t, targeting.Matches(4.99, nil))
+	require.False(t, targeting.Matches(5, nil))
+
+	// 命中第 1 组（balance >= 100 AND 订阅 in [10]）
+	require.False(t, targeting.Matches(100, map[int64]struct{}{}))
+	require.False(t, targeting.Matches(99.9, map[int64]struct{}{10: {}}))
+	require.True(t, targeting.Matches(100, map[int64]struct{}{10: {}}))
+}
+