Toggle to hide tool call activity during streaming

### Describe the feature or problem you'd like to solve

Toggle to hide tool call activity during streaming

### Proposed solution

When the model uses tools, the UI shows intermediate activity like:
"Checking my documentation"
└ # GitHub Copilot CLI Documentation
"Running bash command"
└ ...

This is informative but noisy, especially for quick questions where multiple tools fire.

Request: Add a keybinding (e.g., Ctrl+T style) or /command to toggle between:
1. Show all tool activity (current default)
2. Show only final response text (hidden tool calls) + show in footer/status bar that call activity is hidden

The hidden view would still show the final answer — just hide the intermediate "working on it" indicators. Similar to how Ctrl+T toggles reasoning display.

### Example prompts or workflows

_No response_

### Additional context

_No response_

Start by locating the existing Ctrl+T reasoning-display toggle and the code that renders streaming tool activity. Implement a toggle between full activity and final-response-only output, with hidden status shown in the footer or status bar, and verify both display modes during tool-using prompts.

Written by the indexing model from the issue text.