feat: add local dev + staging environment for testing

[vkaylee]

Changes

• docker-compose.yml: Add key-server-dev service (wrangler dev --local on port 8787)
• dev.sh: Helper script with local + staging commands
• wrangler.jsonc: Add env.staging block for staging worker
• .env.staging.example: Template for staging credentials
• .gitignore: Ignore .env.staging

Usage

Local (no npm/cargo needed — runs in Docker)

./dev.sh up        # Start key-server on port 8787
./dev.sh test-api  # Smoke test
./dev.sh cli 3000  # Run CLI

Staging (Cloudflare)

./dev.sh staging-setup   # One-time: create D1 + deploy
./dev.sh staging-deploy  # Subsequent deploys
./dev.sh staging-test    # Smoke test
./dev.sh staging-cli 3000

All commands run inside Docker container — only Docker required on host.