feat(admin): 新增 C-2 管理员只读监控（概览/人格/记忆/后台思考）

侧边栏「管理员监控」进入的独立管理区 + 独立 Scaffold，四页全部只读，
不调用任何 /admin/* 写端点。

- data：AdminApi（5 条只读 GET）+ AdminDto + AdminRepository，
  经 ApiClientFactory 创建以复用既有 token / 401 处理
- domain：AdminAccess.kt 为权限真源（纯函数，便于单测）；
  AdminFormat.kt 把 RFC3339 与 Unix 毫秒两种时间形状分开解析
- ui：AdminHomeScreen 做成可加页的壳（加页 = AdminPage 加一条枚举），
  四个子页 + 统一失败态；列表项一律 PreferenceCard + BasicComponent
- RBAC：后端契约要求客户端自行降级（api-client §2.0），按矩阵分档——
  viewer 只能进概览/人格；入口禁用 + ViewModel 短路（不发请求）+
  服务端 403 也渲染「无权限」态，三层 fail-closed；
  任何失败都不渲染成「暂无数据」

为什么：M0–M5 + 设置页 C-1 已完成，C-2 是路线上的下一项；后端 5 个读端点
均已实现（非 501），且手机端后续要走「全功能管理」（后端工作小结 主线②，
凭据前置已完成），故管理区做成可扩展的壳而非只读死胡同。

测试：74 个单测全绿，其中新增 29 个
（AdminAccessTest 9 / AdminFormatTest 13 / AdminDtoDecodingTest 7）

app/src/test/kotlin/top/yeij/cyrene/data/api/dto/AdminDtoDecodingTest.kt

@@ -0,0 +1,155 @@
+package top.yeij.cyrene.data.api.dto
+
+import kotlinx.serialization.builtins.ListSerializer
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.boolean
+import kotlinx.serialization.json.int
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import top.yeij.cyrene.data.api.ApiClientFactory
+import top.yeij.cyrene.data.api.ApiEnvelope
+
+/**
+ * 用真实服务端形状的 JSON 校验 DTO 契约（api-client §1/§2）：
+ * `{data}` 信封、开放集合取值、`thinking` 三态、RFC3339 与 Unix 毫秒两种时间。
+ */
+class AdminDtoDecodingTest {
+
+    private val json = ApiClientFactory.json
+
+    private val traceSpans = ListSerializer(AdminTraceSpanDto.serializer())
+    private val personaList = ListSerializer(PersonaSummaryDto.serializer())
+    private val memoryList = ListSerializer(MemorySummaryDto.serializer())
+    private val backthinkList = ListSerializer(AdminBackthinkItemDto.serializer())
+
+    @Test
+    fun `metrics envelope decodes integer-shaped doubles and count maps`() {
+        val body = """
+            {"data":{"totalRequests":12,"qps":3,"avgLatencyMs":10,"maxLatencyMs":40,
+            "perMethod":{"GET":12},"perPath":{"/api/v1/x":12},"statusCounts":{"200":11,"500":1},
+            "llmCalls":2,"subagentEvents":0}}
+        """.trimIndent()
+
+        val data = json
+            .decodeFromString(ApiEnvelope.serializer(AdminMetricsDto.serializer()), body)
+            .data!!
+
+        assertEquals(12L, data.totalRequests)
+        assertEquals(3.0, data.qps, 0.0)
+        assertEquals(10.0, data.avgLatencyMs, 0.0)
+        assertEquals(mapOf("GET" to 12L), data.perMethod)
+        assertEquals(mapOf("200" to 11L, "500" to 1L), data.statusCounts)
+    }
+
+    @Test
+    fun `metrics tolerates missing optional fields`() {
+        val data = json
+            .decodeFromString(ApiEnvelope.serializer(AdminMetricsDto.serializer()), """{"data":{}}""")
+            .data!!
+
+        assertEquals(0L, data.totalRequests)
+        assertTrue(data.perMethod.isEmpty())
+    }
+
+    @Test
+    fun `trace span keeps unknown kind and arbitrary props`() {
+        val body = """
+            {"data":[{"id":"s1","parentId":"s0","name":"loop","kind":"quantum_hop","status":"ok",
+            "startedAt":"2026-03-04T04:34:56Z","endedAt":"2026-03-04T04:34:57Z","durationNs":1000000000,
+            "props":{"model":"gpt","n":3,"flag":true},
+            "events":[{"time":"2026-03-04T04:34:56.123456789Z","type":"retry","props":{"attempt":2}}]}]}
+        """.trimIndent()
+
+        val span = json
+            .decodeFromString(ApiEnvelope.serializer(traceSpans), body)
+            .data!!
+            .single()
+
+        assertEquals("quantum_hop", span.kind)
+        assertEquals("s0", span.parentId)
+        assertEquals(1_000_000_000L, span.durationNs)
+        val props = span.props!!
+        assertTrue(props.isNotEmpty())
+        assertEquals("gpt", (props["model"] as JsonPrimitive).content)
+        assertEquals(3, (props["n"] as JsonPrimitive).int)
+        assertTrue((props["flag"] as JsonPrimitive).boolean)
+        val events = span.events!!
+        assertEquals(1, events.size)
+        assertEquals("retry", events.single().type)
+        assertEquals(2, (events.single().props!!["attempt"] as JsonPrimitive).int)
+    }
+
+    @Test
+    fun `trace span tolerates missing parent and events`() {
+        val span = json
+            .decodeFromString(
+                ApiEnvelope.serializer(traceSpans),
+                """{"data":[{"id":"s1","name":"loop","kind":"llm_call","status":"error","startedAt":"2026-03-04T04:34:56Z","durationNs":1}]}""",
+            )
+            .data!!
+            .single()
+
+        assertNull(span.parentId)
+        assertNull(span.endedAt)
+        assertNull(span.props)
+        assertNull(span.events)
+    }
+
+    @Test
+    fun `persona thinking is absent when unconfigured and keeps tri-state when present`() {
+        val body = """
+            {"data":[
+            {"id":"cyrene","name":"昔涟","character":"memokeeper","isDefault":true,"mode":"chat",
+             "memoryNamespace":"cyrene","mood":"",
+             "thinking":{"budgetTokens":0,"effort":"","showToUser":null,"mode":""}},
+            {"id":"other","name":"?","character":"","isDefault":false,"mode":"telepathy",
+             "memoryNamespace":"","mood":"euphoric"}]}
+        """.trimIndent()
+
+        val personas = json
+            .decodeFromString(ApiEnvelope.serializer(personaList), body)
+            .data!!
+
+        assertEquals(2, personas.size)
+        val configured = personas[0].thinking!!
+        assertNull("null 不能拍平成 false", configured.showToUser)
+        assertEquals(0, configured.budgetTokens)
+
+        assertNull("未配置的人格 thinking 键完全不出现", personas[1].thinking)
+        assertEquals("euphoric", personas[1].mood)
+        // 未知 mode 原样保留，不丢弃、不替换占位符。
+        assertEquals("telepathy", personas[1].mode)
+    }
+
+    @Test
+    fun `memory scope and backthink millis decode as declared`() {
+        val memories = json
+            .decodeFromString(ApiEnvelope.serializer(memoryList), """{"data":[{"id":"m1","scope":"shared","text":"hi"}]}""")
+            .data!!
+        assertEquals("shared", memories.single().scope)
+
+        val backthink = json
+            .decodeFromString(
+                ApiEnvelope.serializer(backthinkList),
+                """{"data":[{"id":"7","trigger":"cron","shouldNotify":true,"pushed":false,"at":1772598896000}]}""",
+            )
+            .data!!
+            .single()
+
+        assertNull(backthink.conclusion)
+        assertTrue(backthink.shouldNotify)
+        assertFalse(backthink.pushed)
+        assertEquals(1_772_598_896_000L, backthink.at)
+    }
+
+    @Test
+    fun `unknown scope is preserved raw instead of being dropped`() {
+        val memories = json
+            .decodeFromString(ApiEnvelope.serializer(memoryList), """{"data":[{"id":"m1","scope":"galaxy","text":"hi"}]}""")
+            .data!!
+        assertEquals("galaxy", memories.single().scope)
+    }
+}