Fix standalone test for direct entrypoints

[PetrNovota]

Summary

• Keep oakctl app run attached while direct-entrypoint apps are monitored.
• Drain app output concurrently instead of closing stdout and waiting immediately.
• Enforce startup/runtime failures and guarantee subprocess cleanup.

Root cause

The standalone harness closed the oakctl output stream and called process.wait() as soon as it saw App output:. Apps launched directly by /entrypoint.sh keep oakctl app run attached for the application lifetime, so the test blocked until the outer CI timeout.

This change retains /entrypoint.sh as the app launcher; runit remains limited to base-image helper services.

Validation

• Targeted standalone test against an OAK4-D R9: 1 passed in 170.22s.
• App reached Pipeline created. and remained running for the configured health interval.
• ruff and ruff-format hooks passed.
• python3 -m py_compile tests/test_examples_standalone.py.
• git diff --check.