Add Arc Receipts MVP

[horn111]

Description

Adds the first Arc Receipts MVP layer to arc-nano-kit.

This introduces invoice/payment ops primitives for Arc apps:

• invoice creation with stablecoin units, payment URI, and Arc memo correlation
• receipt matching for observed payments
• in-memory invoice/receipt/event ledger
• signed webhook helpers
• public @arc-nano-kit/sdk/receipts export
• docs, roadmap, and changelog updates

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

N/A

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have added tests that prove my fix/feature works
• New and existing tests pass locally with my changes
• I have updated the documentation accordingly
• I have updated the CHANGELOG.md

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Project	Deployment	Actions	Updated (UTC)
arc-nano-kit-demo	Ready	Preview, Comment	Jun 18, 2026 11:29pm