refactor: 统一 target name/description 可空语义，前端展示 fallback 到 id

- schema: name/description 允许省略或显式 null，TypeBox Union([Null, String])
- 类型: RawTargetConfig/ResolvedTargetBase/子类型/StoredTarget/TargetStatus name 改为 string | null
- checker resolve: name: t.name ?? null，不再 fallback 到 id
- 语义校验: 拒绝空字符串和纯空白 name
- SQLite: targets.name 列改为可空 TEXT
- 前端: 新增 getTargetDisplayName(target) 展示 name ?? id
- 测试: 覆盖 name/description null 全场景，查找改为按 id
- 文档: 更新 README/DEVELOPMENT 和 6 个 openspec specs

probe-config.schema.json

@@ -110,8 +110,15 @@
             ],
             "properties": {
               "description": {
-                "maxLength": 500,
-                "type": "string"
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 500,
+                    "type": "string"
+                  }
+                ]
               },
               "expect": {
                 "additionalProperties": false,
@@ -416,9 +423,16 @@
                 "type": "string"
               },
               "name": {
-                "maxLength": 30,
-                "minLength": 1,
-                "type": "string"
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 30,
+                    "minLength": 1,
+                    "type": "string"
+                  }
+                ]
               },
               "timeout": {
                 "type": "string"
@@ -511,8 +525,15 @@
             ],
             "properties": {
               "description": {
-                "maxLength": 500,
-                "type": "string"
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 500,
+                    "type": "string"
+                  }
+                ]
               },
               "expect": {
                 "additionalProperties": false,
@@ -658,9 +679,16 @@
                 "type": "string"
               },
               "name": {
-                "maxLength": 30,
-                "minLength": 1,
-                "type": "string"
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 30,
+                    "minLength": 1,
+                    "type": "string"
+                  }
+                ]
               },
               "timeout": {
                 "type": "string"
@@ -720,8 +748,15 @@
             ],
             "properties": {
               "description": {
-                "maxLength": 500,
-                "type": "string"
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 500,
+                    "type": "string"
+                  }
+                ]
               },
               "expect": {
                 "additionalProperties": false,
@@ -893,9 +928,16 @@
                 "type": "string"
               },
               "name": {
-                "maxLength": 30,
-                "minLength": 1,
-                "type": "string"
+                "anyOf": [
+                  {
+                    "type": "null"
+                  },
+                  {
+                    "maxLength": 30,
+                    "minLength": 1,
+                    "type": "string"
+                  }
+                ]
               },
               "timeout": {
                 "type": "string"