Add advanced date and domain filtering

[emmaanuel]

🚀 Enhanced Perplexity MCP Server with Advanced Filtering Capabilities

This PR introduces comprehensive date and domain filtering options to the Perplexity MCP Server, significantly enhancing its search precision and user control.

✨ New Features
Date Filtering System:

• Publication Date Filters: search_after_date_filter and search_before_date_filter for filtering by original publication date
• Last Updated Filters: last_updated_after_filter and last_updated_before_filter for filtering by content modification date
• Recency Filter: search_recency_filter with convenient presets ("day", "week", "month", "year")
• Flexible Combinations: Mix and match filters (except recency with others) for precise time-based searches

Domain Filtering System:

• Allowlist Mode: Include only specified domains/URLs (e.g., ["wikipedia.org", "github.com"])
• Denylist Mode: Exclude unwanted domains using - prefix (e.g., ["-reddit.com", "-pinterest.com"])
• URL-Level Control: Target specific pages for granular filtering
• Subdomain Support: Automatic inclusion of all subdomains

📚 Documentation Enhancements

• 7 Practical Examples: Real-world usage scenarios covering different filtering combinations
• Clear Format Specifications: Detailed date format requirements (M/D/YYYY)
• Usage Guidelines: Important notes on limitations and best practices
• API Consistency: All three tools (perplexity_ask, perplexity_research, perplexity_reason) support the new filters

🎯 Use Cases Enabled

• Academic Research: Filter to trusted sources like arXiv, Nature, Science.org
• Recent Updates: Find documentation updated after specific dates
• Time-bounded Research: Study trends within specific publication periods
• Quality Control: Exclude low-quality sources like forums and social media
• Targeted Documentation: Focus on official docs with recent updates

🔧 Implementation Details

• Backward Compatible: All new parameters are optional
• Input Validation: Clear constraints (max 20 domains, no mixing modes)
• Error Prevention: Built-in restrictions prevent invalid filter combinations
• Type Safety: Proper TypeScript definitions for all new parameters

🌟 User Impact
This enhancement transforms the MCP server from a basic search tool into a sophisticated research assistant, enabling users to:

• Conduct more targeted and relevant searches
• Filter out noise and focus on quality sources
• Perform time-sensitive research with precision
• Customize searches for specific domains or content types

Ready for review! 🚀