feat: introduces the new home for the social controllers

[Bigshmow]

Explanation

This PR adds a new package @metamask/social-controllers to serve as the home for social related controllers (e.g. leaderboard and follow-trading).
Subsequent PRs will add the actual controllers implementations.

Added team-social-ai as the owner in teams.json
Updated .github/CODEOWNERS

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
Low risk: adds a new package scaffold and updates repo metadata/build references, with no production logic changes beyond a placeholder export and test.

Overview
Introduces a new @metamask/social-controllers package as the new home for social-related controllers, including initial TS build/test/docs configuration and a placeholder greeter export with a Jest test.

Wires the package into the monorepo by updating root tsconfig references, yarn.lock, the root README package list/dependency graph, and adds ownership metadata in .github/CODEOWNERS and teams.json (owned by @MetaMask/social-ai).

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[zone-live]

LGTM

[mcmire]

LGTM. Make sure to check out the controller guidelines, guide to creating a data service, and sample-controllers package when implementing this package.

[Bigshmow]

Will do, thanks @mcmire !