refactor(ai_client): migrate _extract_gemini_thoughts + _list_minimax_models (Phase 11 sites 7+8)

Site 7 (_extract_gemini_thoughts):
  try: getattr(resp, 'candidates', None) or [] ... chunks.append(p.text)
  except Exception: pass
  return ''.join(chunks).strip()

Body: pass + empty default '' = SS violation (silent + data loss).

Site 8 (_list_minimax_models):
  try: client.models.list() ... if found: return sorted(found)
  except Exception: pass
  return ['MiniMax-M2.7', 'MiniMax-M2.5', 'MiniMax-M2.1', 'MiniMax-M2']

Body: pass + hardcoded default = SS violation.

New helpers:
- _extract_gemini_thoughts_result(resp) -> Result[str]
  Returns Result(data=thinking_text) on success, Result(data='', errors=[ErrorInfo])
  on attribute access failure.
- _list_minimax_models_result(api_key) -> Result[list[str]]
  Returns Result(data=sorted_models) on success, Result(data=defaults, errors=[ErrorInfo])
  on SDK failure. Defaults extracted to _MINIMAX_DEFAULT_MODELS module constant.

Legacy wrappers delegate to _result helpers and return result.data.

Audit: ai_client SS 7 -> 5. COMPLIANT 29 -> 31.

tests/tier2/phase11_sites78_test.py

@@ -0,0 +1,52 @@
+"""Phase 11 sites 7+8: _extract_gemini_thoughts + _list_minimax_models Result helpers.
+
+Site 7 (_extract_gemini_thoughts):
+    try: candidates = getattr(resp, "candidates", None) or []
+         for ... parts = getattr(content, "parts", None) or []
+             ... if thought: chunks.append(p.text)
+    except Exception: pass
+    return "".join(chunks).strip()
+
+Body: pass + empty default '' = SS violation (silent + data loss).
+
+Site 8 (_list_minimax_models):
+    try: client = OpenAI(api_key=api_key, base_url=base_url)
+         models_list = client.models.list()
+         found = [m.id for m in models_list]
+         if found: return sorted(found)
+    except Exception: pass
+    return ["MiniMax-M2.7", "MiniMax-M2.5", "MiniMax-M2.1", "MiniMax-M2"]
+
+Body: pass + hardcoded default = SS violation.
+"""
+import sys
+sys.path.insert(0, ".")
+
+
+def test_phase11_sites78_extract_gemini_thoughts_result_exists():
+    import src.ai_client
+    assert hasattr(src.ai_client, "_extract_gemini_thoughts_result"), \
+        "_extract_gemini_thoughts_result helper missing"
+
+
+def test_phase11_sites78_list_minimax_models_result_exists():
+    import src.ai_client
+    assert hasattr(src.ai_client, "_list_minimax_models_result"), \
+        "_list_minimax_models_result helper missing"
+
+
+def test_phase11_sites78_helpers_return_result():
+    import src.ai_client
+    import inspect
+    for name in ("_extract_gemini_thoughts_result",
+                 "_list_minimax_models_result"):
+        fn = getattr(src.ai_client, name)
+        sig = inspect.signature(fn)
+        assert "Result" in str(sig.return_annotation), \
+            f"{name} return must be Result, got {sig.return_annotation}"
+
+
+def test_phase11_sites78_legacy_preserved():
+    import src.ai_client
+    assert callable(getattr(src.ai_client, "_extract_gemini_thoughts", None))
+    assert callable(getattr(src.ai_client, "_list_minimax_models", None))