feat(ai_client): add native Ollama adapter; route localhost to it

When _llama_base_url is localhost/127.0.0.1, _send_llama now
calls _send_llama_native (the native /api/chat adapter)
instead of the OpenAI-compat path. The native adapter
supports Ollama's vendor-specific fields: think, images,
thinking.

Functions added (in src/ai_client.py, per the naming
convention HARD RULE on no new src/*.py files):

  ollama_chat(model, messages, *, think='low', images=None,
              tools=None, base_url=OLLAMA_DEFAULT_BASE_URL)
    -> dict[str, Any]

  _send_llama_native(md_content, user_message, base_dir,
                     file_items=None, discussion_history='',
                     stream=False, ...callbacks) -> str

  OLLAMA_DEFAULT_BASE_URL: str = 'http://localhost:11434'

Implementation notes:
- requests loaded via _require_warmed('requests') (local
  scope; preserves startup_speedup_20260606 invariant that
  heavy SDKs are warmed on _io_pool, not imported at module
  level)
- _send_llama dispatches based on 'localhost' in
  _llama_base_url (same check already used by
  _get_llama_cost_tracking at line 2500)
- Removed orphan def stub at the old _send_llama body (the
  dead 'def _build_llama_request' that was overwritten by
  the real one — a known session issue with stale set_file_slice
  edits)
- Native adapter appends the 'thinking' field to history so
  subsequent rounds preserve the reasoning chain

Tests:
- 7 new tests in tests/test_llama_ollama_native.py:
  * ollama_chat hits /api/chat (not /v1/chat/completions)
  * ollama_chat includes 'think' param in payload
  * ollama_chat includes 'images' in payload
  * _send_llama_native wraps ollama_chat
  * _send_llama_native preserves 'thinking' field
  * _send_llama routes localhost to native (no openai client)
  * _send_llama keeps openai path for non-local (no POST)
- Updated test_send_llama_ollama_backend in test_llama_provider.py
  to mock the native path (was: mocked openai-compat; now:
  mocked requests.post)
- 103/103 vendor+tool+provider+import-isolation tests pass
  (no regressions; +7 new tests this commit)
- 4 audit scripts pass

tests/test_llama_provider.py

@@ -17,14 +17,18 @@ def _reset_llama_state():
 def test_send_llama_ollama_backend(monkeypatch: pytest.MonkeyPatch) -> None:
  ai_client._llama_base_url = "http://localhost:11434/v1"
  ai_client.set_provider("llama", "llama-3.2-3b-preview")
- mock_client = MagicMock()
- mock_client.chat.completions.create.return_value = MagicMock(
-  choices=[MagicMock(message=MagicMock(content="hi from ollama", tool_calls=[]))],
-  usage=MagicMock(prompt_tokens=5, completion_tokens=3),
- )
- with patch("src.ai_client._ensure_llama_client", return_value=mock_client):
+ mock_response = MagicMock()
+ mock_response.json.return_value = {
+  "message": {"role": "assistant", "content": "hi from ollama"},
+  "done": True,
+ }
+ mock_requests = MagicMock()
+ mock_requests.post.return_value = mock_response
+ with patch("src.ai_client._require_warmed", return_value=mock_requests):
   result = ai_client._send_llama("system", "user", ".", None, "", False, None, None, None)
-  assert result == "hi from ollama"
+  assert "hi from ollama" in result
+  called_url = mock_requests.post.call_args.args[0]
+  assert called_url == "http://localhost:11434/api/chat"
 
 def test_send_llama_openrouter_backend(monkeypatch: pytest.MonkeyPatch) -> None:
  ai_client._llama_base_url = "https://openrouter.ai/api/v1"