feat: add retryNode with exponential backoff

[haroldfabla2-hue]

Summary

Implements retryNode as a logic primitive that wraps operations with automatic retry logic using exponential backoff.

Features

• Configurable retries (1-10 max attempts)
• Exponential backoff with customizable multiplier (default: 2x)
• Max delay cap to prevent excessive waits (default: 30s)
• Jitter (±10%) to prevent thundering herd problem
• Selective retry via retryOn string patterns
• Zod schemas for input/output validation
• Unit tests included

Input Schema

{
  maxRetries: number;           // 1-10
  initialDelayMs?: number;      // default: 1000
  maxDelayMs?: number;          // default: 30000
  backoffMultiplier?: number;   // default: 2
  retryOn?: string[];           // error patterns to match
  payload?: any;                // pass-through data
}

Files Changed

• packages/nodes/src/logic/retry.ts — Node implementation
• packages/nodes/src/logic/retry.test.ts — Unit tests
• packages/nodes/src/logic/index.ts — Export registration
• packages/nodes/src/index.ts — Top-level export + builtInNodes

Closes #10