Support auditing across multiple GitHub orgs

[raiderrobert]

Problem

Some companies operate multiple GitHub orgs (internal, open source, acquired companies). Auditing ownership across all of them currently requires separate ownrs org runs and manual aggregation.

Current workaround

ownrs org internal-org --format json > internal.json
ownrs org oss-org --format json > oss.json
ownrs org acquired-org --format json > acquired.json
# manually combine/compare

Considerations

• JSON output should include the org name per repo so results from multiple runs can be meaningfully combined
• A future multi-org mode could accept multiple orgs: ownrs org org-a,org-b,org-c
• Cross-org team references add complexity (team exists in org-a but is referenced in org-b's CODEOWNERS)
• Cache should already be per-org (keyed by org name in the cache directory)