Add dev_config.yaml for proxy testing and update AGENTS.md with test collection note

Co-authored-by: Ishaan Jaff <ishaan-jaff@users.noreply.github.com>

AGENTS.md

@@ -217,6 +217,7 @@ See `CLAUDE.md` and the `Makefile` for standard commands. Key notes:
 - The `--timeout` pytest flag is NOT available; don't pass it.
 - Unit tests: `poetry run pytest tests/test_litellm/ -x -vv -n 4`
 - Black `--check` may report pre-existing formatting issues; this does not block test runs.
+- Some test files under `tests/test_litellm/proxy/client/` may fail to collect due to the `responses` module lazy-loading behavior; ignore or skip those directories if collection errors appear.
 
 ### Lint
 

dev_config.yaml

@@ -0,0 +1,13 @@
+model_list:
+  - model_name: fake-openai-endpoint
+    litellm_params:
+      model: openai/my-fake-model
+      api_key: fake-key
+      api_base: https://exampleopenaiendpoint-production.up.railway.app/
+
+general_settings:
+  master_key: sk-1234
+
+litellm_settings:
+  drop_params: True
+  telemetry: False