Expose full tool result content and details in hook tool_result event

Breaking change: ToolResultEvent now exposes content and typed details
instead of just a result string. Hook handlers returning { result: ... }
must change to { content: [...] }.

- ToolResultEvent is now a discriminated union based on toolName
- Each built-in tool has typed details (BashToolDetails, etc.)
- Export tool details types and TruncationResult
- Update hooks.md documentation

Closes #233

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

@@ -1,9 +1,10 @@
-export { bashTool } from "./bash.js";
+export { type BashToolDetails, bashTool } from "./bash.js";
 export { editTool } from "./edit.js";
-export { findTool } from "./find.js";
-export { grepTool } from "./grep.js";
-export { lsTool } from "./ls.js";
-export { readTool } from "./read.js";
+export { type FindToolDetails, findTool } from "./find.js";
+export { type GrepToolDetails, grepTool } from "./grep.js";
+export { type LsToolDetails, lsTool } from "./ls.js";
+export { type ReadToolDetails, readTool } from "./read.js";
+export type { TruncationResult } from "./truncate.js";
 export { writeTool } from "./write.js";
 
 import { bashTool } from "./bash.js";