assistant: Add debug inspector (#16105)

I went with inline approach directly within the panel.
First, enable workflow debugging in the hamburger menu (this works
retroactively as well):


![image](https://github.com/user-attachments/assets/d2ab8edf-bb7b-49a4-8f70-9a6fe94dc7dd)

This enables debug buttons in the header of each step:

![image](https://github.com/user-attachments/assets/3b5d479f-7473-4c41-a2e7-8c10bb71f0ff)
Enabling one pretty-prints the workflow step internals:

![image](https://github.com/user-attachments/assets/e651e826-1270-49ff-8bb6-046c07c006bf)


Release Notes:

- N/A

crates/assistant/src/assistant.rs

@@ -3,6 +3,7 @@
 pub mod assistant_panel;
 pub mod assistant_settings;
 mod context;
+pub(crate) mod context_inspector;
 pub mod context_store;
 mod inline_assistant;
 mod model_selector;