Add service context for treasury

[ahpawel]

Summary

Adds .agents/docs/ to treasury: a short, plain-business-language description of what this service does and which services it interacts with. Documentation only, no code changes.

File	What it says
FUNCTIONS.md	What the service does, as a nested list of business functions
INTERACTIONS.yml	Which AirHelp and third-party services it calls, whose events it listens to, what it publishes
service-card.yaml	Name, kind of application, business domain, short description

Why

The repository is the source of truth for its own context. A GitHub Action copies .agents/docs/ into AirHelp/tech-context (services/treasury/), where it feeds the interactions graph and AI skills. That improves AirHelp Tech Context and agentic workflows for everyone.

What we ask of you

1. ⚠️ Review the files. They were generated by AI, so check they describe how the service works today. Fix anything wrong directly in this PR.
2. Review and merge by October 9.
3. Keep it current. After significant business-logic changes, run /workbench:update-service-context in this repo. It updates only what changed.

References

• File descriptions and the contract: Service context for repositories.
• Writing rules: update-service-context › Artefacts.