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/domain/admin/AdminAccessTest.kt

@@ -0,0 +1,71 @@
+package top.yeij.cyrene.domain.admin
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/** 管理页权限矩阵（api-client §2.0）的客户端降级判定。 */
+class AdminAccessTest {
+
+    @Test
+    fun `owner can use every page`() {
+        AdminPage.entries.forEach { page ->
+            assertTrue(page.name, canAccess(AdminRole.Owner, page))
+        }
+    }
+
+    @Test
+    fun `admin can use every page`() {
+        AdminPage.entries.forEach { page ->
+            assertTrue(page.name, canAccess(AdminRole.Admin, page))
+        }
+    }
+
+    @Test
+    fun `viewer can read monitor pages only`() {
+        assertTrue(canAccess(AdminRole.Viewer, AdminPage.Overview))
+        assertTrue(canAccess(AdminRole.Viewer, AdminPage.Personas))
+    }
+
+    @Test
+    fun `viewer cannot read memories or backthink`() {
+        assertFalse(canAccess(AdminRole.Viewer, AdminPage.Memories))
+        assertFalse(canAccess(AdminRole.Viewer, AdminPage.Backthink))
+    }
+
+    @Test
+    fun `unknown role degrades to viewer`() {
+        assertEquals(AdminRole.Viewer, AdminRole.of("superowner"))
+        assertFalse(canAccess(AdminRole.of("superowner"), AdminPage.Memories))
+    }
+
+    @Test
+    fun `null and blank role degrade to viewer`() {
+        assertEquals(AdminRole.Viewer, AdminRole.of(null))
+        assertEquals(AdminRole.Viewer, AdminRole.of("  "))
+    }
+
+    @Test
+    fun `role parsing tolerates case and surrounding blanks`() {
+        assertEquals(AdminRole.Owner, AdminRole.of(" OWNER "))
+        assertEquals(AdminRole.Admin, AdminRole.of("Admin"))
+        assertEquals(AdminRole.Viewer, AdminRole.of("viewer"))
+    }
+
+    @Test
+    fun `available pages follow the declared order`() {
+        assertEquals(
+            listOf(AdminPage.Overview, AdminPage.Personas),
+            availablePages(AdminRole.Viewer),
+        )
+        assertEquals(AdminPage.entries.toList(), availablePages(AdminRole.Owner))
+    }
+
+    @Test
+    fun `monitor tier is weaker than owner admin tier`() {
+        assertTrue(AdminTier.Monitor.rank < AdminTier.OwnerAdmin.rank)
+        assertTrue(AdminRole.Viewer.rank < AdminRole.Admin.rank)
+        assertTrue(AdminRole.Admin.rank < AdminRole.Owner.rank)
+    }
+}

app/src/test/kotlin/top/yeij/cyrene/domain/admin/AdminFormatTest.kt

@@ -0,0 +1,124 @@
+package top.yeij.cyrene.domain.admin
+
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonPrimitive
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * 两种时间形状 + 未知枚举回落 + 三态展示。
+ *
+ * 时间断言刻意不做时区假设：只比较**同一时刻的两种写法**是否归一，以及是否落成
+ * `yyyy-MM-dd HH:mm:ss` 形态，因此在任何时区的机器上都成立。
+ */
+class AdminFormatTest {
+
+    private val timestamp = Regex("""\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}""")
+
+    @Test
+    fun `offset and zulu spellings of the same instant agree`() {
+        assertEquals(
+            formatRfc3339("2026-03-04T04:34:56Z"),
+            formatRfc3339("2026-03-04T12:34:56+08:00"),
+        )
+    }
+
+    @Test
+    fun `rfc3339 with nanosecond precision parses`() {
+        assertEquals(
+            formatRfc3339("2026-03-04T04:34:56Z"),
+            formatRfc3339("2026-03-04T04:34:56.123456789Z"),
+        )
+    }
+
+    @Test
+    fun `rfc3339 renders as a local timestamp`() {
+        val formatted = formatRfc3339("2026-03-04T04:34:56Z")!!
+        assertTrue(formatted, timestamp.matches(formatted))
+    }
+
+    @Test
+    fun `unparsable rfc3339 is returned raw instead of dropped`() {
+        assertEquals("not-a-time", formatRfc3339("not-a-time"))
+    }
+
+    @Test
+    fun `blank rfc3339 becomes null`() {
+        assertNull(formatRfc3339(null))
+        assertNull(formatRfc3339("   "))
+    }
+
+    @Test
+    fun `backthink millis use the epoch-millis parser, not the rfc3339 one`() {
+        // 同一时刻的两种形状：Unix 毫秒 1772598896000 = 2026-03-04T04:34:56Z
+        assertEquals(
+            formatRfc3339("2026-03-04T04:34:56Z"),
+            formatEpochMillis(1_772_598_896_000L),
+        )
+    }
+
+    @Test
+    fun `nanos pick a unit by magnitude`() {
+        assertEquals("512 ns", formatNanos(512))
+        assertEquals("1.5 µs", formatNanos(1_500))
+        assertEquals("2.5 ms", formatNanos(2_500_000))
+        assertEquals("1.25 s", formatNanos(1_250_000_000))
+    }
+
+    @Test
+    fun `counts are sorted by hits descending`() {
+        assertEquals("GET 5 · POST 2", formatCounts(mapOf("POST" to 2L, "GET" to 5L)))
+    }
+
+    @Test
+    fun `counts keep unknown keys verbatim`() {
+        assertEquals("999 1", formatCounts(mapOf("999" to 1L)))
+    }
+
+    @Test
+    fun `whole doubles lose their decimals`() {
+        assertEquals("12", formatDouble(12.0))
+        assertEquals("0", formatDouble(0.0))
+        assertEquals("1.5", formatDouble(1.5))
+    }
+
+    @Test
+    fun `unknown enum values render raw`() {
+        assertEquals("LLM 调用", traceKindLabel("llm_call"))
+        assertEquals("quantum_hop", traceKindLabel("quantum_hop"))
+        assertEquals("成功", traceStatusLabel("ok"))
+        assertEquals("degraded", traceStatusLabel("degraded"))
+        assertEquals("对话", personaModeLabel("chat"))
+        assertEquals("telepathy", personaModeLabel("telepathy"))
+        assertEquals("人格", memoryScopeLabel("persona"))
+        assertEquals("shared", memoryScopeLabel("shared"))
+        assertEquals("平静", moodLabel("calm"))
+        assertEquals("euphoric", moodLabel("euphoric"))
+    }
+
+    @Test
+    fun `showToUser keeps three distinct states`() {
+        assertEquals("未配置", triStateLabel(null))
+        assertEquals("显示", triStateLabel(true))
+        assertEquals("不显示", triStateLabel(false))
+    }
+
+    @Test
+    fun `props are rendered as compact json without losing keys`() {
+        assertEquals(
+            """{"model":"gpt"}""",
+            formatProps(mapOf<String, JsonElement>("model" to JsonPrimitive("gpt"))),
+        )
+        val two = formatProps(
+            mapOf<String, JsonElement>(
+                "a" to JsonPrimitive(1),
+                "b" to JsonPrimitive(2),
+            ),
+        )!!
+        assertTrue(two, two.contains("\"a\":1") && two.contains("\"b\":2"))
+        assertNull(formatProps(emptyMap()))
+        assertNull(formatProps(null))
+    }
+}