fix(diary): B7 测试套件 + F11 深色模式修复

B7 API 打磨:
- DTO 序列化/反序列化测试 12 个 (Mood/Weather/SyncChange/NotificationType等)
- 测试总数 17 → 29，全部通过
- SyncChange 添加 Serialize derive (测试发现遗漏)

F11 深色模式:
- 修复 mood_page.dart 唯一硬编码颜色 Colors.white → colorScheme.onPrimary
- 全面审计确认所有页面均使用 AppColors/colorScheme，无其他硬编码

验证: cargo test 29/29 ✓ flutter analyze 0 error ✓

app/lib/features/mood/views/mood_page.dart

@@ -213,10 +213,10 @@ class _MoodDistributionChart extends StatelessWidget {
                   color: color,
                   radius: 50,
                   title: '${mc.percentage.toStringAsFixed(0)}%',
-                  titleStyle: const TextStyle(
+                  titleStyle: TextStyle(
                     fontSize: 12,
                     fontWeight: FontWeight.bold,
-                    color: Colors.white,
+                    color: colorScheme.onPrimary,
                   ),
                 );
               }).toList(),

crates/erp-diary/src/dto.rs

@@ -101,7 +101,7 @@ pub struct SyncReq {
 }
 
 /// 同步变更条目
-#[derive(Debug, Deserialize, ToSchema)]
+#[derive(Debug, Serialize, Deserialize, ToSchema)]
 pub enum SyncChange {
     CreateJournal { data: serde_json::Value },
     UpdateJournal { id: uuid::Uuid, version: i32, data: serde_json::Value },
@@ -284,3 +284,150 @@ pub struct AchievementResp {
     pub is_unlocked: bool,
     pub unlocked_at: Option<chrono::DateTime<chrono::Utc>>,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn mood_serializes_to_lowercase() {
+        let json = serde_json::to_string(&Mood::Happy).unwrap();
+        assert_eq!(json, "\"happy\"");
+        let json = serde_json::to_string(&Mood::Thinking).unwrap();
+        assert_eq!(json, "\"thinking\"");
+    }
+
+    #[test]
+    fn mood_deserializes() {
+        let m: Mood = serde_json::from_str("\"calm\"").unwrap();
+        assert!(matches!(m, Mood::Calm));
+        let m: Mood = serde_json::from_str("\"angry\"").unwrap();
+        assert!(matches!(m, Mood::Angry));
+    }
+
+    #[test]
+    fn weather_roundtrip() {
+        let w = Weather::Snowy;
+        let json = serde_json::to_string(&w).unwrap();
+        let back: Weather = serde_json::from_str(&json).unwrap();
+        assert!(matches!(back, Weather::Snowy));
+    }
+
+    #[test]
+    fn create_journal_req_deserializes() {
+        let json = r#"{
+            "title": "测试日记",
+            "date": "2026-06-01",
+            "mood": "happy",
+            "weather": "sunny",
+            "tags": ["日常"],
+            "is_private": true
+        }"#;
+        let req: CreateJournalReq = serde_json::from_str(json).unwrap();
+        assert_eq!(req.title, "测试日记");
+        assert!(req.is_private);
+        assert!(req.class_id.is_none());
+    }
+
+    #[test]
+    fn update_journal_req_minimal() {
+        let req: UpdateJournalReq = serde_json::from_str(r#"{"version": 2}"#).unwrap();
+        assert_eq!(req.version, 2);
+        assert!(req.title.is_none());
+        assert!(req.mood.is_none());
+    }
+
+    #[test]
+    fn notification_type_serializes_snake_case() {
+        assert_eq!(
+            serde_json::to_string(&NotificationType::CommentReceived).unwrap(),
+            "\"comment_received\""
+        );
+        assert_eq!(
+            serde_json::to_string(&NotificationType::AchievementUnlocked).unwrap(),
+            "\"achievement_unlocked\""
+        );
+    }
+
+    #[test]
+    fn sync_change_variants_serialize() {
+        let create = SyncChange::CreateJournal {
+            data: serde_json::json!({"title": "test"}),
+        };
+        let json = serde_json::to_string(&create).unwrap();
+        assert!(json.contains("CreateJournal"));
+
+        let delete = SyncChange::DeleteJournal {
+            id: uuid::Uuid::nil(),
+            version: 3,
+        };
+        let json = serde_json::to_string(&delete).unwrap();
+        assert!(json.contains("DeleteJournal"));
+    }
+
+    #[test]
+    fn conflict_info_serializes() {
+        let info = ConflictInfo {
+            journal_id: uuid::Uuid::nil(),
+            local_version: 1,
+            server_version: 3,
+        };
+        let json = serde_json::to_string(&info).unwrap();
+        assert!(json.contains("\"local_version\":1"));
+        assert!(json.contains("\"server_version\":3"));
+    }
+
+    #[test]
+    fn sticker_pack_resp_serializes() {
+        let resp = StickerPackResp {
+            id: uuid::Uuid::nil(),
+            name: "测试贴纸包".into(),
+            description: None,
+            cover_image_url: None,
+            sticker_count: 10,
+            is_free: true,
+            category: Some("动物".into()),
+        };
+        let json = serde_json::to_string(&resp).unwrap();
+        assert!(json.contains("\"sticker_count\":10"));
+        assert!(json.contains("\"is_free\":true"));
+    }
+
+    #[test]
+    fn mood_count_percentage() {
+        let mc = MoodCount {
+            mood: Mood::Happy,
+            count: 3,
+            percentage: 42.5,
+        };
+        let json = serde_json::to_string(&mc).unwrap();
+        assert!(json.contains("\"percentage\":42.5"));
+    }
+
+    #[test]
+    fn class_member_resp_fields() {
+        let resp = ClassMemberResp {
+            user_id: uuid::Uuid::nil(),
+            role: "student".into(),
+            nickname: Some("小明".into()),
+            joined_at: chrono::Utc::now(),
+        };
+        let json = serde_json::to_string(&resp).unwrap();
+        assert!(json.contains("\"role\":\"student\""));
+    }
+
+    #[test]
+    fn topic_resp_serializes() {
+        let resp = TopicResp {
+            id: uuid::Uuid::nil(),
+            class_id: uuid::Uuid::nil(),
+            teacher_id: uuid::Uuid::nil(),
+            title: "我的周末".into(),
+            description: Some("描述".into()),
+            due_date: None,
+            is_active: true,
+        };
+        let json = serde_json::to_string(&resp).unwrap();
+        assert!(json.contains("\"is_active\":true"));
+    }
+}