chore: set CODEOWNERS

[BigLep]

Setting CODEOWNERS as specified in https://app.notion.com/p/filecoindev/FOC-Engineering-Workstreams-342dc41950c1818f99d2e857a7f3cb2e

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.63%. Comparing base (b6ed4df) to head (2c07704).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #62   +/-   ##
=======================================
  Coverage   52.63%   52.63%           
=======================================
  Files           4        4           
  Lines         342      342           
=======================================
  Hits          180      180           
  Misses        127      127           
  Partials       35       35           

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[BigLep]

@rvagg @Kubuxu: FYI that you are being made a CODEOWNER in this PR.

[Copilot]

Pull request overview

Adds a repository-wide CODEOWNERS file to define default code ownership in line with the referenced FOC Engineering Workstreams proposal.

Changes:

• Introduces .github/CODEOWNERS.
• Sets the default owner for all paths (*) to @rvagg and @Kubuxu.
• Documents the rationale via inline comments and a link to the proposal.

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