threads: order topic chips newest-first beneath General

The gateway already stored a created timestamp per channel/thread but
never sent it over the wire. Now:

- protocol.py: _channel_payload() includes created (unix seconds)
- Protocol.kt: ChannelInfo.created (default 0.0 for legacy gateways)
- ChatScreen: topic switcher sorts threads created-desc (newest right
  after General, swipe new -> old), name as tie-break
- frames.schema.json: document the created field
- ChannelCreatedWireTest: wire deserialization + ordering tests

app/shared/src/commonTest/kotlin/iris/protocol/ChannelCreatedWireTest.kt

@@ -0,0 +1,52 @@
+package iris.protocol
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/** Wire tests for the channel directory `created` field (thread ordering). */
+class ChannelCreatedWireTest {
+    @Test
+    fun channelInfoDeserializesCreated() {
+        val raw =
+            """
+            {"v":1,"type":"channel.created","payload":{"chat_id":"t_9","name":"New topic",
+              "kind":"thread","parent_chat_id":"default","created":1787648374.37}}
+            """.trimIndent()
+        val frame = IrisJson.instance.decodeFromString(Frame.serializer(), raw)
+        val info = frame.payloadAs<ChannelInfo>()
+        assertEquals("t_9", info?.chatId)
+        assertEquals(1787648374.37, info?.created)
+    }
+
+    @Test
+    fun channelInfoDefaultsCreatedToZero() {
+        // Legacy gateways omit the field; the app falls back to name ordering.
+        val raw =
+            """{"v":1,"type":"channel.created","payload":{"chat_id":"t_1","name":"Old","kind":"thread"}}"""
+        val frame = IrisJson.instance.decodeFromString(Frame.serializer(), raw)
+        assertEquals(0.0, frame.payloadAs<ChannelInfo>()?.created)
+    }
+
+    @Test
+    fun threadsSortNewestFirst() {
+        // Mirrors the topic-switcher ordering in ChatScreen: created desc,
+        // name asc as the tie-break (e.g. for legacy entries with created==0).
+        val threads =
+            listOf(
+                ChannelInfo(chatId = "t_2", name = "Capital of Romania", kind = "thread", parentChatId = "default", created = 1787232736.0),
+                ChannelInfo(chatId = "t_1", name = "Capital of France", kind = "thread", parentChatId = "default", created = 1787232221.0),
+                ChannelInfo(
+                    chatId = "t_9",
+                    name = "Test file operations",
+                    kind = "thread",
+                    parentChatId = "default",
+                    created = 1787422924.0,
+                ),
+                ChannelInfo(chatId = "t_0", name = "Legacy b", kind = "thread", parentChatId = "default"),
+                ChannelInfo(chatId = "t_0a", name = "Legacy a", kind = "thread", parentChatId = "default"),
+            )
+        val ordered =
+            threads.sortedWith(compareByDescending<ChannelInfo> { it.created }.thenBy { it.name.lowercase() })
+        assertEquals(listOf("t_9", "t_2", "t_1", "t_0a", "t_0"), ordered.map { it.chatId })
+    }
+}