Update CODEOWNERS: rename team-fm-next to team-fm-foundations

[kparkinson-ld]

Summary

Renames the CODEOWNERS team reference from @launchdarkly/team-fm-next to @launchdarkly/team-fm-foundations to reflect the team rename.

This is part of a batch update across multiple repos in the LaunchDarkly org.

Review & Testing Checklist for Human

• Verify that @launchdarkly/team-fm-foundations is a valid GitHub team in the org and has the expected members

Notes

Repos updated in this batch: ld-find-code-refs, find-code-references-in-pull-request, find-code-references, ld-vscode, ld-openapi. The agent-skills repo was already using the new team name.

Link to Devin session: https://app.devin.ai/sessions/8abe80d07e414755864c1b9c67215686
Requested by: @kparkinson-ld

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