Fix Yes/No response regression for web and images

[carmex]

This PR fixes a regression where GemBot failed to start responses with Yes. or No. for binary questions during web lookups and image generation.

Changes:

• Added isBinaryQuestion utility in src/features/utils.ts.
• Updated Summarizer.summarizeText to accept an optional systemPrompt.
• Updated AIHandler to pass the system prompt to the summarizer for web lookups.
• Updated AIHandler short-circuit logic for image generation to respect binary questions.