feat(cli): skip __init__.py for config-based adk create

[a2105z]

Summary

adk create --type=config no longer writes an empty __init__.py.

Config agents are loaded from root_agent.yaml (after the Python module/package probes miss root_agent). Existing config samples and the YAML agent-loader fixtures already omit __init__.py, so generated projects now match that layout.

Also updates the config success message and CLI unit expectations.

On the package-resolution note in #6753: an empty __init__.py did not expose root_agent either, so the loader still fell through to YAML. With agents_dir prepended on sys.path, the local agent directory remains the first candidate; this change aligns scaffolding with samples rather than relying on an empty package marker.

Fixes #6753

Test plan

• Repro before: adk create --type=config emitted .env, .gitignore, __init__.py, root_agent.yaml
• After: emits .env, .gitignore, root_agent.yaml only
• uv run pytest tests/unittests/cli/utils/test_cli_create.py -q → 36 passed
• Code-type create still generates __init__.py + agent.py

[a2105z]

Hi @ftnext — follow-up on #6753.

adk create --type=config now matches the existing config samples: .env, .gitignore, and root_agent.yaml only (no empty __init__.py). Ready for review whenever maintainers have a chance.