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/find.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 { spawnSync } from "child_process";
 import { existsSync } from "fs";
 import { globSync } from "glob";
@@ -16,6 +16,8 @@ const findSchema = Type.Object({
 	limit: Type.Optional(Type.Number({ description: "Maximum number of results (default: 1000)" })),
 });
 
+export type FindToolInput = Static<typeof findSchema>;
+
 const DEFAULT_LIMIT = 1000;
 
 export interface FindToolDetails {