🛡️ Sentinel: Fix password truncation and command execution loop

[google-labs-jules]

This PR fixes two security/functional issues in copyables/entrypoint.sh:

1. Password Truncation: Passwords with spaces were being split by the shell, resulting in truncated passwords being set for users. Variables are now properly quoted.
2. Command Loop Bug: The loops processing VPNCMD_SERVER and VPNCMD_HUB environment variables were failing to iterate over the command array, resulting in only the first command being executed. This could prevent security configurations (like disabling logs) from being applied.

A regression test script tests/verify_password_fix.sh has been added.

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PR created automatically by Jules for task 14717439191926634042 started by @bluPhy

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