ci: require maintainer review on every path through CODEOWNERS

[AdeGneus]

What does this PR do?

Adds .github/CODEOWNERS with every path defaulting to @AdeGneus, in the same layout as the runtime's. Branch protection on main already requires a code-owner review, and without a CODEOWNERS file that requirement had no owner to name.

Type of change

• feat - new SDK API, model, client, or helper
• fix - bug fix or contract correction
• docs - documentation only
• test - tests only
• refactor - no behavior change
• security - touches signing, validation, install safety, or trust boundaries
• contract-change - changes a cross-repo contract mirrored from ori-specs/runtime

Required checklist

• Linked issue is included below and acceptance criteria are addressed
• pytest -q passes
• mypy ori_sdk tests passes
• ruff check ori_sdk tests passes
• ruff format --check ori_sdk tests passes
• Pre-commit passes for changed files
• Every new .py file has the Apache-2.0 license header
• Public exports in ori_sdk/__init__.py are updated if a public API was added
• Fixtures were added/updated for schema-facing contract changes

Contract and compatibility checklist

• This PR mirrors ori-specs or runtime behavior; it does not redefine runtime authority
• If gateway, hub, health, signing, or skill-package contracts changed, the matching repo/spec PR is linked
• Backward compatibility impact is explained, or the issue explicitly allows a breaking change

Security-sensitive checklist

Not applicable: no signing, install, extraction or validation code changes.

If you used AI assistance

• I can explain every line of AI-generated code in this PR
• I have read and understood every file I modified
• I am not submitting code I cannot defend in review

Related issue

None; repository hardening.

Testing notes

No code changes. GitHub validates the file on the PR (Files changed shows any CODEOWNERS syntax errors); CI runs the existing matrix.