fix: preserve whitespace chunks in stream to fix markdown heading rendering

[Salman-Ahamed]

🎯 What’s this PR about?

Fixes markdown headings rendering as plain text in Chat/Chatbot UIs.

Root cause: parseChunk() used .trim() to validate content, which silently
dropped whitespace-only chunks (e.g., \n\n). This caused headings to glue
to previous text (e.g., Q2## Executive Summary), preventing react-markdown
from parsing them as headings.

Fix: Changed hasContent check from chunk.content.trim() !== '' to
chunk.content !== '' so newline chunks are preserved in the stream output.

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📎 Related ClickUp Ticket

https://app.clickup.com/t/86ewq89f0

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💻 Demo (optional)

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✅ Checklist

• Self-reviewed the code
• Linked the correct ClickUp ticket
• Tested locally (MANDATORY)
• Marked as Draft if not ready for review