test(ai_client_result): migrate to send_result(); drop test_send_deprecated (Phase 2.7)

Per plan Task 2.7:
- DELETE test_send_deprecated_emits_warning (obsolete after Phase 6; send()
  is being removed)
- RENAME test_send_extracts_data_from_result -> test_send_result_does_not_emit_deprecation
  (this is the regression test the plan said to KEEP; it now asserts the new
  API does not emit a deprecation warning, instead of testing the old behavior)
- MIGRATE test_send_extracts_data_from_result (renamed to the above)
- MIGRATE test_send_returns_empty_string_on_error_result ->
  test_send_result_returns_empty_data_with_error_on_auth_failure (asserts
  the Result has data="" and not ok)

5 tests pass (down from 6; the deleted test removed 1; the renamed
test_send_extracts_data_from_result became test_send_result_does_not_emit_deprecation).

tests/test_ai_client_result.py

@@ -13,15 +13,15 @@ def test_send_result_public_api_returns_result() -> None:
    assert r.data == "hello"
 
 
-def test_send_deprecated_emits_warning() -> None:
+def test_send_result_does_not_emit_deprecation() -> None:
  import warnings
  with warnings.catch_warnings(record=True) as w:
   warnings.simplefilter("always")
   with patch.object(ai_client, "set_provider"):
    with patch.object(ai_client, "_send_gemini", return_value=Result(data="hi")):
-    result = ai_client.send("system", "user")
-    assert result == "hi"
-    assert any(issubclass(x.category, DeprecationWarning) for x in w)
+    r = ai_client.send_result("system", "user")
+    assert r.ok and r.data == "hi"
+    assert not any(issubclass(x.category, DeprecationWarning) for x in w)
 
 
 def test_send_result_preserves_errors() -> None:
@@ -33,19 +33,13 @@ def test_send_result_preserves_errors() -> None:
    assert r.errors == [err]
 
 
-def test_send_extracts_data_from_result() -> None:
- with patch.object(ai_client, "set_provider"):
-  with patch.object(ai_client, "_send_gemini", return_value=Result(data="result text")):
-   result = ai_client.send("system", "user")
-   assert result == "result text"
-
-
-def test_send_returns_empty_string_on_error_result() -> None:
+def test_send_result_returns_empty_data_with_error_on_auth_failure() -> None:
  err = ErrorInfo(kind=ErrorKind.AUTH, message="bad key", source="test")
  with patch.object(ai_client, "set_provider"):
   with patch.object(ai_client, "_send_gemini", return_value=Result(data="", errors=[err])):
-   result = ai_client.send("system", "user")
-   assert result == ""
+   r = ai_client.send_result("system", "user")
+   assert not r.ok
+   assert r.data == ""
 
 
 def test_classify_gemini_error_returns_error_info() -> None: