fix: improve system prompt and tool argument validation

[ilonae]

Fixes #1345

Features

• Improve system prompt to discourage unnecessary tool use for simple queries
• Added validation for missing required tool arguments with informative error messages

Feature Docs

N/A - Bug fix for existing functionality

Influence
This fix addresses a critical usability issue where simple factual questions (e.g., "where is Boston?") would trigger unnecessary tool calls without required parameters, resulting in TypeErrors.

Impact:

• Simple queries now receive direct answers without tool invocation
• When tools are called, missing required arguments are caught early with clear error messages
• Agent can better self-correct when tools are invoked incorrectly
• Improved developer experience with more informative error logs

Result
Before fix:
TypeError: PythonExecute.execute() missing 1 required positional argument: 'code'

After fix:
Simple query: "where is Boston?"

• Agent answers directly without attempting to use python_execute
• If tool is called without parameters, error message explains the issue:
  "Tool 'python_execute' was called with missing required arguments.
  missing 1 required positional argument: 'code'.
  Please ensure all required parameters are provided when calling this tool."