fix(config): reload .env over stale shell overrides

[teknium1]

Summary

• load Hermes env files through a shared helper that lets ~/.hermes/.env override stale shell-exported values on restart
• preserve user env over project fallback while still letting the project .env fill missing values in dev setups
• wire the shared loader into the main startup entrypoints and add regression coverage for the reported stale-BASE_URL/provider case

Root cause

I reproduced the issue directly on current main:

• shell had stale OPENAI_BASE_URL=https://old.example/v1
• ~/.hermes/.env contained OPENAI_BASE_URL=https://new.example/v1 and HERMES_INFERENCE_PROVIDER=custom
• importing hermes_cli.main left the old shell values in place because the startup dotenv loads were using the default override=False

That meant editing .env and restarting Hermes could still leave the process pinned to old model/provider/base_url settings if those vars were already exported in the parent shell.

Test plan

• source .venv/bin/activate && python -m pytest tests/hermes_cli/test_env_loader.py tests/test_runtime_provider_resolution.py -n0 -q
• source .venv/bin/activate && python -m pytest tests/test_cli_provider_resolution.py tests/hermes_cli/ -n0 -q
• source .venv/bin/activate && python -m pytest tests/gateway/ -n0 -q
• source .venv/bin/activate && python -m pytest tests/ -n0 -q # one unrelated existing full-suite failure remains: tests/test_api_key_providers.py::TestResolveProvider::test_auto_detects_minimax_cn_key

Verification

• PYTHONPATH=. python /tmp/repro1244.py now prints the updated values from the Hermes user env file instead of the stale shell exports