IAV-252/refactor: Implement category-based instruction management architecture

Overview

This MR introduces a significant architectural change to the instruction management system by implementing a category-based hierarchy for standard instructions and improving the response structure for custom instructions.

Key Changes

🏗️ Architecture

• Introduced AgentStandardInstructionCategory entity to organize instructions hierarchically
• Instructions are now automatically initialized when agents are created
• All standard instructions are grouped by categories

🔄 API Changes (Breaking)

Custom Instructions

• GET /agents/agent-custom-instructions/agent/{agentUid} now returns grouped response:
  • Separates suggestions and restrictions
  • Includes agent information and statistics
  • Response type: AgentCustomInstructionsByCategoryResponse

Standard Instructions

• GET /agents/agent-standard-instructions/agent/{agentUid} returns category hierarchy
• POST /agent-standard-instructions is now a bulk update endpoint (not creation)
• New category-level endpoints:
  • PATCH /{categoryUid}/activate
  • PATCH /{categoryUid}/deactivate
• Removed: Individual instruction retrieval by UID

✨ New Features

• Automatic instruction initialization during agent creation
• Bulk configuration update with category and instruction-level control
• Category-level activation/deactivation
• Enhanced statistics in custom instruction responses

🔧 Refactoring

• Consolidated validation logic in AgentValidationHelper
• Simplified initializeDefaultLanguages by accepting agent entity
• Removed redundant languagesCount validation parameter
• Improved error handling with helper methods

Related Issues

Closes IAV-252