Update sig-directory.md

Adding Nikos Andrikogiannopoulos (Metrika) to the Regulatory Compliance SIG based on experience in digital asset risk management, operational risk monitoring, and institutional blockchain infrastructure oversight.

Relevant background includes work with financial institutions, tokenization initiatives, GBBC RMF operationalization efforts, and prior participation in the CFTC Technology Advisory Committee.

Development Fund Proposal Submission

Proposal file: Link to the proposal added in this PR (e.g., /proposals/your-proposal-name.md)

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Summary

Briefly describe the proposal and the value it delivers to the Canton ecosystem (2–3 sentences).

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Checklist

• [ ] Proposal file added under /proposals/
• [ ] Milestones and funding amounts defined
• [ ] Acceptance criteria included
• [ ] Alignment with Canton priorities described

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Notes for Reviewers

(Add anything the Tech & Ops Committee should pay attention to.)