Report all validation errors at once instead of one-at-a-time

[data-douser]

Context

Sub-issue of #208 — Area 1: Validation errors revealed one-at-a-time

Problem

When multiple required parameters are missing from a tool invocation (e.g. audit_store_findings, annotation_create), the JSON Schema validator returns an error for only the first missing field. After supplying that field and re-invoking, a second missing field is reported, and so on. This forces iterative trial-and-error to discover the full parameter contract and wastes tool invocations.

Example with audit_store_findings:

1. Invoked without owner → must have required property 'owner'
2. Added owner, re-invoked → must have required property 'sourceLocation'

Requirements

• Enable allErrors: true (or equivalent) in the JSON Schema validator so all violations are reported in one response
• Aggregate multiple validation errors into a single, clear error message (e.g. must have required properties: 'owner', 'sourceLocation')