feat: add Docker deployment, UAT test suites, and fix signup middleware bug

- Add Dockerfile, docker-entrypoint.sh, and .dockerignore for containerized deployment
- Fix middleware to exclude /api/tenants/signup from auth (P0 signup bug)
- Add Playwright E2E tests (16 browser tests) and curl-based API test script (80 tests)
- Add playwright config and dev dependency
- Update .gitignore with proper exclusions
- Add v1 milestone audit report and ISP system PRD

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package-lock.json

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