M1+M2: gateway core loop + agent transparency

M1 (gateway core loop / text round-trip):
- WS server (ws_server.py): bind, hello auth (constant-time), hello.ack, heartbeat, connection registry
- pairing.py: token generation, pairing store, QR payload
- adapter.py: send() -> message frame; inbound message.send -> MessageEvent -> handle_message
- app: Connect screen, GatewayClient (connect + reconnect), ChatScreen send/render, SecureStore (Android/Desktop)
- tests/ws_probe.py: probe harness driving a real turn

M2 (streaming + reasoning + tools + commentary):
- protocol.py: M2 frame types (message.start/update/stop, tool.start/progress/end, commentary)
- adapter.py: per-chat turn-state machine; classify outbound into frames; _split_reasoning; tool-line parsing
- reasoning in streaming: capture via on_stream_delta hook (kind=reasoning, gated by plugins.stream_reasoning_deltas) with a FIFO barrier, attach to message.stop
- app: live streaming bubble, ReasoningBlock (collapse + copy), ToolCard (Everything/Truncated/Nothing), dimmed commentary, typing
- docs/14-milestones.md: M1/M2 marked done; reasoning note corrected

app/build.gradle.kts

@@ -2,6 +2,7 @@ plugins {
     kotlin("multiplatform") version "2.1.0" apply false
     kotlin("android") version "2.1.0" apply false
     kotlin("jvm") version "2.1.0" apply false
+    kotlin("plugin.serialization") version "2.1.0" apply false
     id("com.android.application") version "8.7.3" apply false
     id("com.android.library") version "8.7.3" apply false
     id("org.jetbrains.compose") version "1.7.3" apply false