Display tool execution results in terminal

[spachava753]

Summary

Adds visibility into tool execution by displaying results to stderr during agent runs. Users can now see what data tools return, making it easier to verify tool behavior and debug issues when the agent acts on incorrect information.

Changes

Tool results are now printed to stderr with glamour markdown rendering:

• JSON responses are automatically pretty-printed in json code blocks
• Code execution output appears in shell code blocks
• Results are truncated to 20 lines to keep output manageable
• Styling is consistent with the response printer

Implementation

• Added tool callback wrapper that intercepts tool results and prints them
• Integrated wrapper into the generator middleware chain
• Created shared content renderer helper for consistent styling
• Added table-driven tests for various tool result scenarios

Example Output

Regular MCP Tool:

#### Tool "get_weather" result:
```json
{
  "condition": "sunny",
  "temperature": 72
}
```

Code Execution:

#### Code execution output:
```shell
Reading file data.txt...
Found 5 matches.
```

Closes #105