feat: add code note type and migrate to Upstash Redis + Piston

[typelets]

Summary

Adds support for 'code' note type and migrates infrastructure to Upstash Redis + Piston. Reduces costs by ~$40-47/month while maintaining full backward compatibility.

Changes

1. Code Note Type Support

• Added "code" as a third note type alongside "note" and "diagram"
• Updated schema, validation, OpenAPI docs, and integration tests
• Defaults to "note" if type not specified (backward compatible)

2. Cache Migration (ElastiCache → Upstash Redis)

• Replaced ioredis Cluster with Upstash REST client
• Eliminates ElastiCache Serverless ($3.60/mo) and VPC endpoints ($44/mo)
• Upstash uses pay-per-request pricing ($0-10/mo)
• Added cache invalidation when emptying trash

3. Code Execution Migration (Judge0 → Piston)

• Migrated from Judge0 RapidAPI to self-hosted Piston
• Changed from async polling to synchronous execution
• Maintains Judge0-compatible API (no frontend changes needed)
• Supports 14 languages
• Deprecated /api/code/status/:token endpoint (returns 410)

[typelets]

🎉 This PR is included in version 1.14.0 🎉

The release is available on GitHub release

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