Design principles adherence audit across all domain repos

## Summary

Once the design principles are established ([RFC #93](https://github.com/beckn/protocol-specifications-v2/issues/93)), all domain repos (`beckn/mobility`, `beckn/logistics`, `beckn/DEG`, and others) must be audited for adherence.

## Audit checklist per repo

- [ ] No `$ref` or `$id` URIs pointing back to `protocol-specifications-v2` (one-way dependency rule)
- [ ] All `$id` values follow canonical URL pattern `https://schema.beckn.io/{domain}/{SchemaName}/v2.0`
- [ ] All `$ref` URIs use versioned canonical form (no bare URLs, no relative paths)
- [ ] `@context` defaults point to `https://schema.beckn.io/` (not `schema:X` class URIs)
- [ ] `@type` defaults use `beckn:` prefix (not `schema:` prefix)
- [ ] No `schema:X` property keys (only in `x-jsonld '@id'` annotations)
- [ ] `additionalProperties: false` on all `type: object` schemas (except intentionally open ones)
- [ ] All JSON Schema files use `$schema: "https://json-schema.org/draft/2020-12/schema"`

## Output

A per-repo audit report filed as issues in each repo with specific violations and fixes.

## Depends on

- RFC #93 (principles document must be final before auditing against it)
- Issues #2–#8 in `core_schema` (establishes the corrected baseline to audit against)

@abhimail @ameetdesh @nirmay @bachia @anandp504 @pramodkvarma