feat: add URL indexing directly from chat input

[taprosoft]

Description

• Add URL indexing directly from chat input
• Enable LightRAG collection by default
• Optimize batching logic for LightRAG & NanoGraphRAG
• Add warning message for empty GRAPHRAG_API_KEY

Type of change

• New features (non-breaking change).
• Bug fix (non-breaking change).
• Breaking change (fix or feature that would cause existing functionality not to work as expected).

Checklist

• I have performed a self-review of my code.
• I have added thorough tests if it is a core feature.
• There is a reference to the original bug report and related work.
• I have commented on my code, particularly in hard-to-understand areas.
• The feature is well documented.