feat(chat): image specialist legacy lane, Responses fixes, ACL + UI attachments

- Image expert: DashScope-style /chat/completions via image_legacy_client; early exit in
  direct_loop when skill_binding_role is image; shared placeholder helper; docs/IMAGE_SPECIALIST_LANE.md.
- Strict attachment ACL: link_attachment_acl on assistant chat_message rows (sqlite_store);
  chat attachment rate limit when user_id empty; admin chat tests updated.
- Admin chat UI: aggregate bubbles render assistant_text attachments (image_ref); WS expand path.
- turn_runner: persisted_chat_attachments_nonempty for final_msg selection.
- OpenAI Responses transport + agent_messages/agent_core_attempt adjustments; env docs and tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/LLM_TRANSPORTS.md

@@ -30,6 +30,11 @@ Transport selection happens in `oclaw/runtime/agents/factory.py`.
 - **Streaming**: output text deltas via `on_token` → WS `chat.delta`
 - **Key**: profile secret or `OPENAI_API_KEY`
 
+### Chat UI「图片专家」（绕行本矩阵）
+
+- **Not** a separate profile transport: when the user selects specialist **`image`** in `/chat`, `runtime/direct_loop.py` takes an early return and calls **`platform/llm/image_legacy_client.send_legacy_image_messages`** (DashScope-style `/chat/completions`), so that turn does **not** use `OpenAIResponsesModel` / chat transports above.
+- Details, env vars, ACL, and UI hooks: **`docs/IMAGE_SPECIALIST_LANE.md`**.
+
 ### `anthropic` (Anthropic Messages streaming)
 - **Transport**: `oclaw/platform/llm/transports/anthropic_messages.py::AnthropicMessagesModel`
 - **API**: Anthropic `messages.stream` surface (gateway must provide Anthropic-compatible protocol)