Fix duplicate service registration and simplify EnvFile logic

[Copilot]

Addresses code review feedback on the Docker Compose deployment PR.

Test fixes:

• Removed duplicate IResourceContainerImageBuilder service registration in DockerComposePublisherTests.cs that would cause DI container conflicts

Code simplification:

• Refactored EnvFile.AddOrUpdate to eliminate duplicate assignment in if/else branches by checking onlyIfMissing condition upfront

Before:

if (_entries.ContainsKey(key))
{
    if (onlyIfMissing) return;
    _entries[key] = new EnvEntry(key, value, comment);
}
else
{
    _entries[key] = new EnvEntry(key, value, comment);  // Duplicate
}

After:

if (_entries.ContainsKey(key) && onlyIfMissing)
{
    return;
}
_entries[key] = new EnvEntry(key, value, comment);

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