Ship initial community decision packs with fixtures

[Sunny-commit]

Goal

Provide reusable, reviewable decision contracts for repeated agent problems.

Packs

• security/prompt_injection.yaml
• rag/hallucination_gate.yaml
• agent/action_guard.yaml
• support/escalation.yaml

Acceptance criteria

• Each pack has precise, non-overlapping labels and a concise description.
• Representative positive, negative, and ambiguous fixtures are included.
• Schema validation and unit tests are added.
• Known failure modes and calibration assumptions are documented.
• Ambiguous consequential actions default to review or blocking.

Dependency

Coordinate with the evaluation-harness issue before claiming production readiness.