Add Roil Canton liquidity primitive proposal

Add Roil proposal for the Canton Development Fund.

This proposal requests 800,000 CC over 16 weeks to develop an open-source, reusable Canton-native liquidity primitive and validate it through the Roil reference implementation.

The proposal includes:

• Canton-native liquidity core and reserve accounting
• Asset integration and liquidity provision flows
• Quote calculation, swap execution and settlement
• Authorization and validation workflows
• Concurrent transaction and contention testing
• Canton network validation
• Roil reference integration
• Automated tests and technical documentation
• Independent security review, remediation and final open-source release

SIG: defi-liquidity Champion: Seeking a Champion

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.)