fix(shared): validate singular interface field in connects relationships

[Copilot]

Description

calm validate silently accepted references to non-existent interfaces in connects relationships when using the singular "interface": "string" form. The Spectral rules only validated the plural "interfaces": [] array form, but all real-world architecture files (including the canonical calm-1.json/calm-2.json) use the singular form — making interface validation a no-op in practice.

Root cause: interfaceIdExistsOnNode short-circuited on !input.interfaces, so singular interface strings were never checked. No Spectral rule targeted the singular field path.

Changes

• interface-id-exists-on-node.ts — collects desired interfaces from both interface (string) and interfaces (array) before validating against the target node; previously bailed out if interfaces was absent
• rules-architecture.ts — adds referenced-interface-defined-in-architecture rule targeting $.relationships[*].relationship-type.connects.*.interface (singular path) via existing interfaceIdExists function
• interface-id-exists-on-node.spec.ts — adds 4 tests covering singular interface: valid reference, interface not on target node, and target node with no interfaces

Before (no error reported):

{
  "connects": {
    "source": { "node": "node-a" },
    "destination": { "node": "node-b", "interface": "non-existent-interface" }
  }
}

After:

Referenced interface with ID 'non-existent-interface' was not defined on the node with ID 'node-b'.

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
• 🎨 Code style/formatting changes
• ♻️ Refactoring (no functional changes)
• ⚡ Performance improvements
• ✅ Test additions or updates
• 🔧 Chore (maintenance, dependencies, CI, etc.)

Affected Components

• CLI (cli/)
• Schema (calm/)
• CALM AI (calm-ai/)
• CALM Hub (calm-hub/)
• CALM Hub UI (calm-hub-ui/)
• CALM Server (calm-server/)
• CALM Widgets (calm-widgets/)
• Documentation (docs/)
• Shared (shared/)
• VS Code Extension (calm-plugins/vscode/)
• Dependencies
• CI/CD

Commit Message Format ✅

Testing

• I have tested my changes locally
• I have added/updated unit tests
• All existing tests pass

Checklist

• My commits follow the conventional commit format
• I have updated documentation if necessary
• I have added tests for my changes (if applicable)
• My changes follow the project's coding standards

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.