fix(controller): reserve unique frontend ports per run

[emmepra]

Summary

• reserve a unique frontend port per run and persist it in the run binding
• reuse the reserved port for launch, read-models, and restart-stack
• add focused controller coverage for reserved frontend ports

Checks

• PYTHONPATH=. pytest tests/test_run_launcher_frontend_ports.py tests/test_run_frontend_ports.py tests/test_public_runs_routes.py -q
• python3.11 -m compileall app
• bash scripts/up_stack.sh
• live verification with 3 overlapping hello-world runs, each receiving a distinct frontend URL and completing successfully