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/read.ts

@@ -13,7 +13,7 @@ const readSchema = Type.Object({
 	limit: Type.Optional(Type.Number({ description: "Maximum number of lines to read" })),
 });
 
-interface ReadToolDetails {
+export interface ReadToolDetails {
 	truncation?: TruncationResult;
 }