fix: revert explicit apikey header (caused Kong duplicate-apikey 401)

The previous commit added apikey to _create_base_client headers, but supabase-py
already sets apikey from the key arg → two apikey headers → Kong rejected every
as-user call with 401 'Duplicate API key found' (exam API 502'd on auth). Revert
to Authorization-only; fix the two header unit tests to assert the real contract
(apikey via the key arg; options.headers carries only the user Authorization).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

tests/test_me_bootstrap.py

@@ -122,11 +122,11 @@ def test_supabase_client_for_user_uses_access_token_authorization(monkeypatch):
 
     assert anon.access_token == "user-token"
     assert captured["url"] == "http://supabase.test"
+    # apikey is supplied via the `key` positional arg (supabase-py sets the apikey header from it).
+    # options.headers must carry ONLY the per-user Authorization override — adding apikey here too
+    # produces a duplicate apikey header that Kong rejects ("Duplicate API key found").
     assert captured["key"] == "anon-key"
-    assert captured["options_kwargs"]["headers"] == {
-        "apikey": "anon-key",
-        "Authorization": "Bearer user-token",
-    }
+    assert captured["options_kwargs"]["headers"] == {"Authorization": "Bearer user-token"}
 
 
 def test_no_school_bootstrap_requires_school_membership_but_allows_canvas():