Bring up :proto protocol + :server (Ktor) + :client (HTTP) modules; wire :server into standalone with EchoProtoAgent

Major additions:

* :proto (KMP submodule) — in-house stateful protocol replacing AG-UI.
  Agent owns conversation transcript; Conversation.events(after) is a live,
  replay-free stream; backfill via Conversation.getMessages(after, offset, limit).
  Each Event carries an Instant date for client-side resume tracking.
  Sealed hierarchies (Content/Message/Event/AgentEvent) annotated @Serializable
  with snake_case @SerialName JSON discriminators so the wire format is
  decoupled from Kotlin class names.

* :server (JVM, Ktor 3.1.3) — REST+SSE facade for Agent.
  Public entry: Route.agentikAgent(agent, path = "/agentik").
  Endpoints: create/list/get/patch/delete conversations, POST messages (202),
  POST interrupt, GET messages, GET conversation events (SSE),
  GET agent events (SSE), GET /health. Custom Instant serializer for
  kotlin.time.Instant registered contextually on agentikJson (ISO-8601,
  ignoreUnknownKeys=true, explicitNulls=false).

* :client (JVM, Ktor HTTP Client + CIO) — mirror of :server returning
  a pw.binom.agentik.proto.Agent backed by HTTP calls. Custom SSE parser
  since ktor-client-sse is not on the 3.1.3 client classpath.

* standalone — EchoProtoAgent (in-memory Agent for :proto), EchoAgent
  (existing AG-UI echo), both mounted on the same Netty embedded server
  on port 8080 (/agui and /agentik); A2A stays on its own CIO engine on
  8081. EchoProtoAgent smoke-tested end-to-end against :server: all 11
  endpoints, including live SSE delivery of StartResponse/AppendText/End
  event triplets and Agent-level Created/Deleted events.

Design notes pinned in:
* agentik/IRC-QUESTIONS.md — closed 13-item checklist for the upcoming
  :irc-server transport (channel = conversation, CTCP for structural
  events, draft/chathistory for backfill, ImageStore side-channel, etc).
* docs/ARCHITECTURE.md — overall layout snapshot.

gradle/libs.versions.toml

@@ -0,0 +1,40 @@
+[versions]
+kotlin = "2.4.20"
+kotlinx-serialization = "1.11.0"
+kotlinx-coroutines = "1.11.0"
+kotlinx-datetime = "0.8.0"
+ktor = "3.1.3"
+agui = "0.1.0"
+a2a = "1.0.0-SNAPSHOT"
+
+[plugins]
+kotlin-multiplatform = { id = "org.jetbrains.kotlin.multiplatform", version.ref = "kotlin" }
+kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
+kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }
+
+[libraries]
+# --- AG-UI (pw.binom.agui) — KMP: jvm + native ---
+agui-api = { module = "pw.binom.agui:api", version.ref = "agui" }
+agui-client = { module = "pw.binom.agui:client", version.ref = "agui" }
+agui-server = { module = "pw.binom.agui:server", version.ref = "agui" }
+
+# --- A2A (pw.binom.a2a) — shared: KMP (jvm + linuxX64); client/server: JVM-only ---
+a2a-shared = { module = "pw.binom.a2a:shared", version.ref = "a2a" }
+a2a-client = { module = "pw.binom.a2a:client", version.ref = "a2a" }
+a2a-server = { module = "pw.binom.a2a:server", version.ref = "a2a" }
+
+# --- Ktor (сервер, JVM) ---
+ktor-server-core = { module = "io.ktor:ktor-server-core", version.ref = "ktor" }
+ktor-server-sse = { module = "io.ktor:ktor-server-sse", version.ref = "ktor" }
+ktor-server-netty = { module = "io.ktor:ktor-server-netty", version.ref = "ktor" }
+ktor-server-content-negotiation = { module = "io.ktor:ktor-server-content-negotiation", version.ref = "ktor" }
+ktor-serialization-kotlinx-json = { module = "io.ktor:ktor-serialization-kotlinx-json", version.ref = "ktor" }
+ktor-client-core = { module = "io.ktor:ktor-client-core", version.ref = "ktor" }
+ktor-client-cio = { module = "io.ktor:ktor-client-cio", version.ref = "ktor" }
+ktor-client-content-negotiation = { module = "io.ktor:ktor-client-content-negotiation", version.ref = "ktor" }
+
+# --- commons ---
+kotlinx-coroutines-core = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-core", version.ref = "kotlinx-coroutines" }
+kotlinx-serialization-core = { module = "org.jetbrains.kotlinx:kotlinx-serialization-core", version.ref = "kotlinx-serialization" }
+kotlinx-serialization-json = { module = "org.jetbrains.kotlinx:kotlinx-serialization-json", version.ref = "kotlinx-serialization" }
+kotlinx-datetime = { module = "org.jetbrains.kotlinx:kotlinx-datetime", version.ref = "kotlinx-datetime" }