Write 'Why we built OpenDecree' blog post for Dev.to

[zeevdr]

Description

Write the launch blog post explaining the problem OpenDecree solves, design decisions, and what exists vs why it wasn't enough. This is the HN-compatible deep-dive and the first piece of launch content.

Acceptance criteria

• Published on Dev.to
• Covers: the problem (business config is too important for KV stores, too dynamic for deploys)
• Design decisions: schema-first, Go, gRPC, multi-tenant
• Includes schema → SDK code example
• Links to GitHub repo

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Migrated from zeevdr/decree#152