Add JSON Agents import/export support

Summary

Add support for importing and exporting agent configurations using the JSON Agents specification.

Description

JSON Agents is an open standard for defining AI agent configurations in a portable, interoperable format. Adding support for this specification would allow users to:

• Export their configured agents and patterns to a standardized JSON format
• Import agent definitions from other tools that support the JSON Agents spec
• Share agent configurations with the community
• Version control agent definitions alongside their codebase

Proposed Features

Import

• Import JSON Agents files (.json) via UI file picker or drag-and-drop
• Validate imported configurations against the JSON Agents schema
• Map JSON Agents properties to HLLM's internal agent configuration format
• Support importing single agents or collections

Export

• Export individual agent configurations to JSON Agents format
• Export entire patterns (with all agents) as a JSON Agents collection
• Include prompts, model preferences, and pattern-specific settings

Reference

• JSON Agents Specification: https://jsonagents.org/

Tasks

• [ ] Research JSON Agents schema and mapping to HLLM agent types
• [ ] Implement import parser and validator
• [ ] Implement export serializer
• [ ] Add UI for import/export (buttons in Agent Configuration panel)
• [ ] Add validation error feedback for malformed imports
• [ ] Write tests for import/export roundtrip