fix: remove db migration from Dockerfile build step

[stuburger]

tl;dr: Database migrations should run at deployment time, not build time, to avoid race conditions and build failures.

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Remove database migration from Dockerfile build step

Problem

The Dockerfile was running yarn db:migrate during the image build process (line 54), which is an anti-pattern that can cause several issues:

• Build failures when database is not available during image build
• Race conditions in multi-instance deployments where multiple containers try to migrate simultaneously
• Environment coupling making the image less portable across different environments
• Deployment complexity mixing build-time and runtime concerns

Solution

Removed the RUN yarn db:migrate command from the Dockerfile. Database migrations should be handled at deployment time, not build time.

Deployment Impact for Mercur users

This change requires updating the deployment pipeline to run migrations separately:

# Recommended deployment sequence:
1. Build Docker image
2. Deploy infrastructure (SST/Terraform/Pulumi/etc)
3. Run database migrations: yarn db:migrate
4. Start application containers

Benefits

• ✅ Safer deployments - no migration race conditions
• ✅ Portable images - same image works across all environments
• ✅ Reliable builds - builds don't depend on database availability
• ✅ Better separation of concerns - build vs runtime operations
• ✅ Easier rollbacks - migrations can be managed independently
• ✅ Dockerfile builds successfully without database connection
• ✅ Image can be deployed and migrations run separately
• ✅ No functional changes to the application itself