feat(node-type-registry): add max_depth parameter to EventReferral

[pyramation]

Summary

Adds max_depth to EventReferral's parameter_schema in the node-type-registry package. This enables the downstream generator in constructive-db to build multi-level referral chain walks.

Change: One new property in packages/node-type-registry/src/event/referral.ts:

max_depth: {
  type: 'integer',
  description: 'Maximum depth to walk up the invite chain. Default 1 (direct inviter only). Set 2–10 to enable multi-level referral rewards. App-level only — must not be combined with entity_field.',
  default: 1,
  minimum: 1,
  maximum: 10,
}

The generator implementation that consumes this is in constructive-db PR #1261.

Closes constructive-io/constructive-planning#904

Review & Testing Checklist for Human

• Verify the property position (before auto_register_type, after entity_field) is consistent with other node types
• Confirm the min/max/default values are reasonable (1–10, default 1)

Notes

This is a purely additive schema change — no existing behavior changes since the default is 1 (today's single-hop behavior). The downstream constructive-db PR has the generator implementation + integration tests.

Link to Devin session: https://app.devin.ai/sessions/2ad5d38ab24e4d43ba283eb9ae8b5c81
Requested by: @pyramation

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