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/grep.ts

@@ -31,7 +31,7 @@ const grepSchema = Type.Object({
 
 const DEFAULT_LIMIT = 100;
 
-interface GrepToolDetails {
+export interface GrepToolDetails {
 	truncation?: TruncationResult;
 	matchLimitReached?: number;
 	linesTruncated?: boolean;