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/smartchat.interfaces.ts

@@ -0,0 +1,52 @@
+import type { LanguageModelV3, ModelMessage, ToolSet, IAgentRunResult } from './plugins.js';
+
+/**
+ * Options for creating a ChatSession.
+ */
+export interface IChatSessionOptions {
+  /** The language model to use */
+  model: LanguageModelV3;
+  /** System prompt for the agent */
+  system?: string;
+  /** Tools available to the agent */
+  tools?: ToolSet;
+  /** Maximum agentic steps per turn */
+  maxSteps?: number;
+}
+
+/**
+ * Callbacks for real-time streaming events during a turn.
+ */
+export interface IChatCallbacks {
+  /** Called for each streamed text token */
+  onToken?: (delta: string) => void;
+  /** Called when a tool call starts */
+  onToolCall?: (name: string, input: unknown) => void;
+  /** Called when a tool call completes */
+  onToolResult?: (name: string, result: string) => void;
+  /** Called when a turn completes */
+  onTurnComplete?: (result: IAgentRunResult) => void;
+  /** Called on error */
+  onError?: (error: Error) => void;
+}
+
+/**
+ * Events emitted during chat.
+ */
+export type TChatEvent =
+  | { type: 'token'; delta: string }
+  | { type: 'tool_call_start'; name: string; input: unknown }
+  | { type: 'tool_call_end'; name: string; result: string }
+  | { type: 'turn_start' }
+  | { type: 'turn_complete'; result: IAgentRunResult }
+  | { type: 'error'; error: Error };
+
+/**
+ * Usage stats accumulated across all turns.
+ */
+export interface IChatUsage {
+  inputTokens: number;
+  outputTokens: number;
+  totalTokens: number;
+  turns: number;
+}