Complete Phase 5 integration, CI, and deployment hardening

[slapiar]

Summary

This PR completes the Phase 5 delivery for the security refactoring work and prepares the project for a final release.

What changed

• add 45 integration tests covering router, API flows, and end-to-end scenarios
• add performance benchmark automation for core file manager operations
• add GitHub Actions quality workflow for tests, linting, static analysis, audit, Docker build, and smoke validation
• optimize Docker and Compose runtime for PHP 8.3, health checks, non-root execution, and persistent mounts
• add deployment runbook plus smoke and health check scripts
• update project status and Phase 5 planning documents
• bump release version to 2.7.0

Validation

• benchmark script passes its targets locally
• Docker image builds successfully
• smoke check passes against the built container
• health check returns HTTP 200