fix: self-service signup, unified key store, persistent data volume

- Added /v1/signup/free endpoint for instant API key provisioning
- Built unified key store (services/keys.ts) with file-based persistence
- Refactored auth middleware to use key store (no more hardcoded env keys)
- Refactored usage middleware to check key tier from store
- Updated billing to use key store for Pro key provisioning
- Landing page: replaced mailto: link with signup modal
- Landing page: Pro checkout button now properly calls /v1/billing/checkout
- Added Docker volume for persistent key storage
- Success page now renders HTML instead of raw JSON
- Tested: signup → key → PDF generation works end-to-end

docker-compose.yml

@@ -13,5 +13,10 @@ services:
       - STRIPE_WEBHOOK_SECRET=${STRIPE_WEBHOOK_SECRET}
       - BASE_URL=${BASE_URL:-https://docfast.dev}
       - PRO_KEYS=${PRO_KEYS}
+    volumes:
+      - docfast-data:/app/data
     mem_limit: 512m
     cpus: 1.0
+
+volumes:
+  docfast-data: