## Summary
Fixes the ordering-dependent test failure in `test_custom_provider_display_name.py` (issue #754).
**Root cause:** `_models_with_cfg()` patches `config.cfg` then calls `get_available_models()`. That function checks `config.yaml`'s mtime on every call — if it has changed since the last `reload_config()`, it calls `reload_config()` again, which reads from disk and silently overwrites the patch. Any test that writes `config.yaml` (e.g. via `save_settings()`) before this test runs changes the mtime and triggers the reload.
**Fix:** Pin `config._cfg_mtime` to the current `config.yaml` mtime before calling `get_available_models()`, then restore it in the `finally` block. This is the same pattern already used in `test_model_resolver.py` (lines 249, 393).
**Also restores `_cfg_mtime`** in the `finally` block so the patch leaves no side effects on subsequent tests.
## Tests
1510 passed — the previously-flaky test now passes regardless of which tests ran before it.
Closes#754
When a custom_providers entry in config.yaml has a 'name' field (e.g. 'Agent37'),
the web UI model picker now uses that name as the group header instead of the
generic 'Custom' label.
Previously all custom_providers entries were bucketed under 'custom' which
rendered as 'Custom' in the dropdown optgroup — losing the named identity the
user set up during onboarding.
Changes:
- Track named custom providers as 'custom:<slug>' keys internally so multiple
named providers can coexist as separate groups
- When building model groups, emit each named provider under its own display
name (e.g. 'Agent37') rather than falling through to the generic label
- Unnamed entries (no 'name' field) still fall back to the 'Custom' group
- When all entries are named, the bare 'Custom' bucket is suppressed
Adds 7 tests covering single named provider, multiple named providers,
multiple models in same named provider, unnamed fallback, and mixed cases.
Fixes#557
