[GOVERNANCE] Create digdir/agent-registry repo and define .agent-card.yml standard

## As a developer or IT architect at Digdir
## I want a standard way to declare and register a production agent
## So that the organisation has a verified, up-to-date inventory of all running agents and their owners

## Business Goal

Without a registry, there is no operational baseline for governance. Teams cannot be held accountable for agents they haven't formally declared. An `.agent-card.yml` standard gives every API-based agent a machine-readable identity file that supports discovery, monitoring, and incident response — and establishes the pattern for future Digdir-built AI products.

## Acceptance Criteria

- The `digdir/agent-registry` GitHub repository exists under the `digdir` org
- A documented `.agent-card.yml` schema is published in the repo, covering at minimum:
- Agent name and version
- Owning team and primary contact
- Model ID and provider
- Runtime environment
- Declared scope and permissions
- Kill-switch contact and escalation path
- A reference template `.agent-card.yml` file exists in the repo
- Contributing guidelines explain how any team registers their agent — submissions are gated by KITT review
- Schema validation approach is defined (tooling decision deferred to Tech Lead)

## Prerequisites

⚠️ Prerequisite: Creation of `digdir/agent-registry` repo under the `digdir` GitHub org — Owner: Tech Lead (Adi)

⚠️ Prerequisite: Schema validation tooling — Owner: Tech Lead (Adi)

## Dependencies

- Part of #74 — `[GOVERNANCE] Establish Minimum Viable Agentic AI Governance — KITT Team`

## Estimate

2–3 days