docs(client): add «Кэш списка бесед» section + ios targets to :journal-inmemory

- :journal-inmemory — added iosX64/iosArm64/iosSimulatorArm64 to the
  target set so :storage-inmemory (which now depends on it) can build
  for iOS. Pure `MutableMap`+`Mutex` impl, no I/O, fully portable.

- client/README.md — new «Кэш списка бесед» section:
  - shows `agent.conversationStore` as the read-only entry point;
  - demonstrates the «remote.listFlow → local.upsert + outbox.agentEvents
    → local apply» pattern (Created/Renamed/Touched/Deleted);
  - notes that the cache is built into `AgentikAgent` by default;
  - mentions `wrapWithLocalConversationCache` for custom stores (SQLite/JSON);
  - points to `agentikHttpClient(...).raw` as the escape-hatch for clients
    that want direct HTTP.

Also adds `HttpConversationStore.kt` to the index (the file existed on
disk but wasn't `git add`ed in the previous commit).

client/src/commonMain/kotlin/pw/binom/agentik/client/HttpConversationStore.kt

@@ -0,0 +1,58 @@
+package pw.binom.agentik.client
+
+import io.ktor.client.HttpClient
+import io.ktor.client.call.body
+import io.ktor.client.request.get
+import io.ktor.client.request.parameter
+import io.ktor.http.HttpStatusCode
+import pw.binom.agentik.journal.ConversationRecord
+import pw.binom.agentik.journal.ConversationStore
+
+/**
+ * HTTP-реализация [ConversationStore] (read-only metadata view),
+ * ходящая в `:server`-фасад.
+ *
+ * **Endpoint**: `GET {baseUrl}/conversations?offset=&limit=` —
+ * возвращает `List<ConversationRecord>` (id, title, isTemporal, createdAt,
+ * updatedAt) БЕЗ handle'ов и image-support флагов (это лёгкая проекция
+ * для UI-списка; handle берётся через `agent.getConversation(id)`).
+ *
+ * **Read-only**: запись в `conversation` table — только через команды
+ * `agent.createConversation / deleteConversation / renameConversation`.
+ *
+ * Клиентский кэш строится композицией `HttpConversationStore` (snapshot)
+ * + `agent.outbox.agentEvents(after)` (live deltas: Created/Deleted/
+ * Renamed/Touched) — см. `client/README.md` секция
+ * «Кэш списка бесед».
+ */
+internal class HttpConversationStore(
+    private val httpClient: HttpClient,
+    private val baseUrl: String,
+) : ConversationStore {
+
+    private val agentUrl: String = baseUrl.trimEnd('/')
+
+    override suspend fun get(id: String): ConversationRecord? {
+        val response = httpClient.get("$agentUrl/conversations/$id")
+        if (response.status == HttpStatusCode.NotFound) return null
+        check(response.status == HttpStatusCode.OK) {
+            "conversationStore.get($id): server returned ${response.status}"
+        }
+        return response.body<ConversationRecord>()
+    }
+
+    override suspend fun list(offset: Int, limit: Int): List<ConversationRecord> {
+        val response = httpClient.get("$agentUrl/conversations") {
+            parameter("offset", offset)
+            parameter("limit", limit)
+        }
+        check(response.status == HttpStatusCode.OK) {
+            "conversationStore.list: server returned ${response.status}"
+        }
+        return response.body<List<ConversationRecord>>()
+    }
+
+    override fun close() {
+        // HttpClient закрывает владелец (AgentClient / AgentikAgent).
+    }
+}