Updating the delivery dates for the open source reference wallet grant proposal

Updating the delivery dates for the open source reference wallet grant proposal based on grant proposal approval

Development Fund Proposal Submission

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

---

Summary

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

---

Checklist

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

---

Notes for Reviewers

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