MCP tool errors lose ErrorData and become HTTP 500 with traceback

## Problem
When calling MCP tools through the runtime HTTP API, tool failures are surfaced as a generic HTTP 500 string, and the original MCP `ErrorData` (especially `data`) is lost. The error message also includes a full traceback, which is noisy for end users.

This makes it hard for adapters like `sandbox_tool_adapter` to display the real error cause (e.g., `invalid patch: The last line of the patch must be '*** End Patch'`).

## Examples (actual outputs)
Initial error (only HTTP error string):
```json
[{"type": "text", "text": "500 Server Error: Internal Server Error for url: http://localhost:49156/fastapi/mcp/call_tool"}]
```

After adding custom handling on the client side, we can see more detail, but it is still wrapped in a 500 error + traceback and `ErrorData.data` is lost:
```json
[{"type": "text", "text": "MCP tool call failed: apply_patch\nstatus=500\nendpoint=http://10.10.2.200:49156/fastapi/mcp/call_tool\ndetail:\ninvalid patch: Traceback (most recent call last):\n File \"/agentscope_runtime/routers/mcp.py\", line 162, in call_tool\n result = await server.call_tool(tool_name, arguments)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File \"/agentscope_runtime/routers/mcp_utils.py\", line 158, in call_tool\n result = await self.session.call_tool(tool_name, arguments)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File \"/agentscope_runtime/venv/lib/python3.11/site-packages/mcp/client/session.py\", line 277, in call_tool\n return await self.send_request(\n ^^^^^^^^^^^^^^^^^^^^^^^^\n File \"/agentscope_runtime/venv/lib/python3.11/site-packages/mcp/shared/session.py\", line 294, in send_request\n raise McpError(response_or_error.error)\nmcp.shared.exceptions.McpError: invalid patch\n"}]
```

Current workaround in our stack (not ideal; just shows we are forced to flatten the error ourselves):
```json
[{"type": "text", "text": "{\"code\":\"INVALID_PARAMS\",\"data\":{\"error\":\"invalid patch: The last line of the patch must be '*** End Patch'\"},\"message\":\"invalid patch\"}"}]
```

## Expected behavior
For MCP tool errors, preserve the original `ErrorData` (code/message/data) and avoid wrapping it into an HTTP 500 + traceback. Ideally, the runtime should return a normal `CallToolResult` with `isError=true` and put the structured error into `structuredContent`, so client adapters can display meaningful error details without custom hacks.

## Suspected locations
- `src/agentscope_runtime/sandbox/box/shared/routers/mcp.py` catches all exceptions and raises `HTTPException` with `detail=traceback`, which discards `ErrorData.data`.
- `src/agentscope_runtime/sandbox/client/http_client.py` returns only `str(e)` on non-2xx responses, so the response body is lost even if it contains error details.

## Question
Is the intended design to surface tool failures via `CallToolResult.isError=true` rather than raising HTTP 500? If so, I can prepare a PR to:
1) Convert `McpError` to `CallToolResult` in the runtime router, preserving `code/message/data`.
2) Improve the HTTP client to parse error responses when non-2xx.

Would this be acceptable to maintainers?