feat(quickstart): add one-shot compose, fake recon mode, demo emitter…

[coryli]

What

• Add 10-minute Quickstart via docker-compose with API + Workers
• Implement env-guarded fake reconciliation mode to generate drift without Stripe
• Provide Node demo emitter that sends usage, runs reconciliation, saves CSV
• Update README with Quickstart; add CI workflow to smoke-test Quickstart

Why

• Enables new users to get a drift report in under 10 minutes with zero code changes
• Lowers onboarding friction and validates core parity loop quickly
• Gives contributors a reproducible flow to test reconciliation behavior locally

Test Plan

• docker compose -f docker-compose.quickstart.yml up -d --build
• Verify API readiness: curl -fsS http://localhost:3000/health/ready
• Run emitter (auto via compose demo or locally): node examples/demo-emitter/index.js
• Confirm CSV created: examples/demo-emitter/output/drift_report.csv
• Check CSV header: head -n1 examples/demo-emitter/output/drift_report.csv | grep 'subscription_item_id,period,local,stripe,drift_abs,drift_pct,status'
• CI: .github/workflows/quickstart-smoke.yml runs the same and asserts header

Related Issues

• closes 10-minute Quickstart + Demo Emitter #78

[geminimir]

@coryli quickstart ci you introduced is still failing... I need you to look at that before mergin this PR..

[geminimir]

@coryli could you still take care of this?