What does this PR do?

Fixes agent_label and description in generated .agent files always showing hardcoded defaults ("New Agent" and "New agent description") instead of reflecting the user-provided --name flag. The agentSpec argument is now always passed to ScriptAgent.createAuthoringBundle() with name, developerName, and role set from user input, with role falling back to the spec file's value when a spec is provided.

What issues does this PR fix or reference?

@W-21220597@

Functionality Before

Running sf agent generate authoring-bundle --no-spec --name "My Agent" --api-name MyAgent produced:

agent_label: "New Agent"
description: "New agent description"

Functionality After

Running the same command now produces:

agent_label: "My Agent"
description: "My Agent description"

When a spec file with a role field is provided, that value is used for description instead.

Testing Setup Notes

• Run sf agent generate authoring-bundle --no-spec --name "Test Agent" --api-name TestAgent --target-org <org> and verify the .agent file has agent_label: "Test Agent" and description: "Test Agent description"
• Run with --spec <path-to-spec> where the spec has a role field, and verify description matches the spec's role
• NUT tests updated with assertions for agent_label and description in both with-spec and no-spec cases