gateway: let member keys reach the Metis pass-through route

LiteLLM gates auth=true pass-through routes behind allowed_passthrough_routes,
a LiteLLM Enterprise field: on this community-edition proxy the management API
refuses to set it, so no member key can ever be granted access, and auth:false
would instead expose the route (and our GreenPT key) to anonymous callers.

Add patch_passthrough_key_access.py (house style: build-time, non-fatal,
idempotent, compile-checked) so routes the operator names in
general_settings.coop_passthrough_open_to_keys are callable by ANY
authenticated key. Authentication itself is unchanged: auth=true still installs
Depends(user_api_key_auth), so unauthenticated requests are still rejected.

Validated locally against LiteLLM 1.103.2: a plain generated key gets 200 with
real Metis answers; an unauthenticated POST gets 401.

config.yaml

@@ -251,6 +251,16 @@ general_settings:
   # per-token billing (reading usage.input_tokens from the Metis response) would
   # need a patch in the house style of the existing patch_*.py files; until then
   # treat the spend figure for this route as an approximation, not an invoice.
+  # Routes here (matched by prefix) may be called by ANY authenticated member
+  # key. LiteLLM's own gate for auth=true pass-through routes
+  # (`allowed_passthrough_routes`) is an Enterprise-only field, so on this
+  # community-edition proxy it can never be granted to member keys — the only
+  # other option, auth:false, would expose the route publicly and forward the
+  # co-op's GreenPT key to anonymous callers. This list is consumed at build
+  # time by patch_passthrough_key_access.py; authentication is unchanged (the
+  # endpoint still requires a valid key).
+  coop_passthrough_open_to_keys:
+    - "/v1/systemone"
   pass_through_endpoints:
     - path: "/v1/systemone"
       target: "https://api.greenpt.ai/v1/systemone"