🔧 chore: recreate requirements/ directory structure for Heroku compatibility

- Create requirements/main.txt with base dependencies (no dev, no production groups)
- Create requirements/production.txt with production-specific dependencies (psycopg)
- Update requirements.txt to reference both files (-r requirements/main.txt -r requirements/production.txt)

This maintains Heroku compatibility while using the modern pyproject.toml + uv workflow.
The requirements files are auto-generated from uv.lock using:
- uv export --no-dev --no-group production -o requirements/main.txt
- uv export --only-group production -o requirements/production.txt

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: matrixise