* feat(config): support ${ENV_VAR} substitution in config.yaml
* fix: extend env var expansion to CLI and gateway config loaders
The original PR (#2680) only wired _expand_env_vars into load_config(),
which is used by 'hermes tools' and 'hermes setup'. The two primary
config paths were missed:
- load_cli_config() in cli.py (interactive CLI)
- Module-level _cfg in gateway/run.py (gateway — bridges api_keys to env vars)
Also:
- Remove redundant 'import re' (already imported at module level)
- Add missing blank lines between top-level functions (PEP 8)
- Add tests for load_cli_config() expansion
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Co-authored-by: teyrebaz33 <hakanerten02@hotmail.com>
