chore: add foundations team to CODEOWNERS

[dianab-cl]

Summary

• Adds @cosmos/foundations-team as a code owner to ensure the foundations team is automatically assigned as reviewers on PRs.

Linked issue

ITS-1231

[linear-code]

ITS-1231

[greptile-apps]

Greptile Summary

This PR updates global code ownership for the repository. The main change is:

• Adds @cosmos/foundations-team as a global CODEOWNERS owner.

Confidence Score: 4/5

The change is small but affects reviewer assignment across the whole repository and needs adjustment before merging.

Only one CODEOWNERS file changed, and the ownership behavior is straightforward to assess.

.github/CODEOWNERS

T-Rex Logs

What T-Rex did

• Reproduced CODEOWNERS behavior for README.md by running a last-match reproduction script against the repository's CODEOWNERS, which showed the line 3 rule with @cosmos/foundations-team won and the existing owner was not preserved.
• Before and after CODEOWNERS resolution were captured: before the README.md matched the base rule with foundations_team_present: NO, after it matched the head rule with foundations_team_present: YES, and both runs exited with code 0.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "chore: add @cosmos/foundations-team to C..." | Re-trigger Greptile}

[greptile-apps]

Preserve existing owners
GitHub applies only the last matching CODEOWNERS pattern, so this second ** entry replaces @cosmos/stack-team instead of adding another reviewer group. For any changed file, only @cosmos/foundations-team will be requested; put both teams on the same ** line to keep the existing owner.

[mergify]

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