refactor(schemas): 统一 message/notification 命名边界，旧名收敛至兼容映射表

- notification 域：渠道能力（MessageChannel→NotificationChannel、ChannelCapability* 迁入 notification.py）
- message 域：消息收发（Notification→Message、NotificationType→MessageType、CommingMessage→IncomingMessage、NotificationHistoryItem→MessageHistoryItem、NotificationClear*→MessageClear*）
- Agent 工具契约：send_notification_message→send_message、notification_callback→message_callback
- 源码不保留旧名物理别名，旧导入经 app/runtime/compat/manifest.py SYMBOL_ALIASES 惰性解析
- API 路径与持久化键冻结不变，前端零改动
- 新增兼容守护测试与 docs/rules/07 命名边界规范

tests/test_legacy_import_compat.py

@@ -20,6 +20,7 @@ from app.runtime.compat.manifest import (
     SYMBOL_ALIASES,
     VIRTUAL_PACKAGES,
     ModuleAlias,
+    _MESSAGE_NOTIFICATION_SYMBOL_ALIASES,
 )
 
 
@@ -316,7 +317,7 @@ def test_plugin_scan_reports_moved_symbol_import(tmp_path: Path):
 
 
 def test_symbol_alias_manifest_covers_all_moved_public_symbols():
-    """符号级映射清单应覆盖媒体身份与整理工作项的旧入口。"""
+    """符号级映射清单应覆盖媒体身份、整理工作项与消息/通知命名统一的旧入口。"""
     assert set(SYMBOL_ALIASES["app.domain.media"]) == {
         "MEDIA_SOURCE_ALIASES",
         "MEDIA_SOURCE_PREFIXES",
@@ -329,8 +330,15 @@ def test_symbol_alias_manifest_covers_all_moved_public_symbols():
     assert set(SYMBOL_ALIASES["app.schemas"]) == {
         "TransferTask",
         "TransferQueue",
-    }
+    } | set(_MESSAGE_NOTIFICATION_SYMBOL_ALIASES)
     assert set(SYMBOL_ALIASES["app.schemas.transfer"]) == {
         "TransferTask",
         "TransferQueue",
     }
+    assert set(SYMBOL_ALIASES["app.schemas.types"]) == {
+        "MessageChannel",
+        "NotificationType",
+    }
+    assert set(SYMBOL_ALIASES["app.schemas.message"]) == set(
+        _MESSAGE_NOTIFICATION_SYMBOL_ALIASES
+    )