chore: add agent rules file

[Lexpeartha]

Adds AGENTS.md at the project root to provide better context to coding agents

[zsculac]

Looks pretty good @Lexpeartha. A couple of ideas to improve (not all need to be included now, I'll try to sort them by priority):

1. Instructions for the agent to do after implementing any feature/fix/improvement - e.g. linting, formatting, add new tests if useful, running tests and fixing them if the change broke them
3. withSourceKnowledgeAssets return when possible to include KA in the responses
4. registering MCP prompts and resources