feat(coding-agent): type ToolCallEvent.input per tool

Matches ToolResultEvent pattern with typed inputs via discriminated union.

- Export *ToolInput types from tool schemas
- Add *ToolCallEvent interfaces for each built-in tool
- Add isToolCallEventType() guard with overloads for built-ins

Direct narrowing (event.toolName === "bash") doesn't work due to
CustomToolCallEvent.toolName: string overlapping with literals.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/coding-agent/src/core/tools/ls.ts

@@ -1,5 +1,5 @@
 import type { AgentTool } from "@mariozechner/pi-agent-core";
-import { Type } from "@sinclair/typebox";
+import { type Static, Type } from "@sinclair/typebox";
 import { existsSync, readdirSync, statSync } from "fs";
 import nodePath from "path";
 import { resolveToCwd } from "./path-utils.js";
@@ -10,6 +10,8 @@ const lsSchema = Type.Object({
 	limit: Type.Optional(Type.Number({ description: "Maximum number of entries to return (default: 500)" })),
 });
 
+export type LsToolInput = Static<typeof lsSchema>;
+
 const DEFAULT_LIMIT = 500;
 
 export interface LsToolDetails {