Write 'Schema-first: define once, get everything' blog post

[zeevdr]

Description

The shareable "aha moment" post. Show a single YAML schema and then all the things that fall out of it: typed APIs, Go/Python/TS SDKs, Admin UI, validation, audit trail, docs.

Acceptance criteria

• Published on Dev.to
• Visual progression: schema YAML → Go SDK → Python SDK → TypeScript SDK → Admin UI → CLI
• Explains the "define once" philosophy
• Shareable on Twitter/Reddit

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Migrated from zeevdr/decree#153