chore: add code owners

[MichaelSaucier]

Adds .github/CODEOWNERS with @MichaelSaucier as the global code owner so the existing required Code Owner review branch protection has an ownership map to enforce.

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[MichaelSaucier]

Review verdict: no findings.

Reviewed head 901811e7401c0b43ba0b0642872d5ab1a1407378. The diff adds only .github/CODEOWNERS with * @MichaelSaucier, which is the intended minimal ownership map needed for the existing required Code Owner review branch protection to have effect. Build & Test is green. This is not a self-approval; the protected branch still requires a human/non-author approval before merge.