feat(hooks): add delegate-task-english-directive hook to enforce English for subagents

Appends bold uppercase English-only directive to explore, librarian,
oracle, and plan subagent prompts via tool.execute.before on the task tool.

src/hooks/index.ts

@@ -52,3 +52,4 @@ export { createWriteExistingFileGuardHook } from "./write-existing-file-guard";
 export { createHashlineReadEnhancerHook } from "./hashline-read-enhancer";
 export { createJsonErrorRecoveryHook, JSON_ERROR_TOOL_EXCLUDE_LIST, JSON_ERROR_PATTERNS, JSON_ERROR_REMINDER } from "./json-error-recovery";
 export { createReadImageResizerHook } from "./read-image-resizer"
+export { createDelegateTaskEnglishDirectiveHook } from "./delegate-task-english-directive"