fix: SQLite default value compatibility and docker/nginx networking

[phreakocious]

Summary

• SQLite compatibility: Patches Column.__init__ to neutralize PostgreSQL-specific server_default values (gen_random_uuid(), NOW()) that SQLite can't handle, enabling local development with SQLite
• Docker networking: Updates nginx.conf upstream names from backend/frontend to openagents-workspace/openagents-frontend to match actual container names in docker-compose
• Frontend build: Adds NEXT_PUBLIC_API_URL as a build arg in the frontend Dockerfile so the API URL is baked in at build time rather than requiring runtime configuration
• API URL fallback: Changes || to ?? for NEXT_PUBLIC_API_URL fallback across api.ts, auth.ts, and dashboard-api.ts so empty string is respected (not treated as falsy)
• Fetch caching: Removes cache: 'no-store' from the base fetch wrapper to allow normal browser/CDN caching behavior

Test plan

• Run workspace backend locally with SQLite — confirm tables create without errors
• docker compose up — verify nginx routes to backend and frontend correctly
• Build frontend Docker image with custom NEXT_PUBLIC_API_URL — confirm it's used at runtime
• Confirm API calls work with the ?? fallback change

🤖 Generated with Claude Code

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