feat: implement bonding curve milestone API

[Tekprecious]

Closes #970

Summary

• Implemented GET /api/v1/keys/:keyId/curve/milestones API endpoint to provide the full bonding curve milestone configuration and current progress.
• Computes currentPrice and tracks the progress of currentSupply against all configured MILESTONES.
• Dynamically identifies the nextMilestone based on the active position on the bonding curve.
• Introduces an isGraduated flag to signal when the currentSupply reaches or exceeds the final milestone threshold.
• Refreshes milestone data with a 30-second TTL polling cache to optimize lookups and prevent unnecessary DB reads.

Testing

• pnpm lint
• pnpm build
• pnpm exec prisma generate when schema or generated types changed

Checklist

• Linked issue or backlog item
• No secrets or live credentials added
• Docs updated if setup or env changed
• Change is scoped to one problem

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