feat(initial): scaffold @push.rocks/smartchat with core, CLI, and web layers

Three-layer architecture built on @push.rocks/smartagent:
- ts/ — ChatSession wrapping runAgent() with conversation state management
- ts_cli/ — ink-based terminal chat TUI (React.createElement, no JSX)
- ts_web/ — Lit web components (smartchat-window, smartchat-message, smartchat-input)

ts/plugins.ts

@@ -0,0 +1,7 @@
+// @push.rocks/smartagent
+import { runAgent } from '@push.rocks/smartagent';
+export { runAgent };
+export type { IAgentRunOptions, IAgentRunResult } from '@push.rocks/smartagent';
+
+// @push.rocks/smartai (types re-exported from ai SDK)
+export type { LanguageModelV3, ModelMessage, ToolSet } from '@push.rocks/smartai';