feat: add diagram type support with filtering and tests

[typelets]

Changes

• ✅ Add type field filtering to GET /api/notes endpoint
• ✅ Support querying notes by type (note or diagram)
• ✅ Add TypeScript type safety for type field in handlers
• ✅ Add comprehensive test coverage for diagram functionality
• ✅ Document default behavior in OpenAPI schema

Technical Details

• The type field defaults to 'note' for backwards compatibility with existing clients
• The index on type column (already applied in production) enables efficient filtering
• All validation happens at both the validation layer and OpenAPI schema level

Test Coverage

Added 4 new integration tests:

1. Default type behavior (creates 'note' when not specified)
2. Explicit diagram note creation
3. Filtering notes by type
4. Updating note type from note to diagram

Backwards Compatibility

Fully backwards compatible - existing API clients will continue to work without changes. Notes created without specifying type will automatically default to 'note'.

[typelets]

🎉 This PR is included in version 1.12.0 🎉

The release is available on GitHub release

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