Add support for multiple document paths with glob patterns

[badri]

This enhancement allows users to specify multiple document directories and glob patterns in config.json, providing more flexibility in organizing and indexing markdown files.

Features:

• Config: Changed from single 'documents_dir' to 'document_patterns' array
• Supports both directory paths and glob patterns (e.g., "./docs/**/*.md")
• Backwards compatible: old 'documents_dir' automatically migrated
• Sync: Uses pattern matching to find files instead of single directory walk
• MCP tools: Updated path validation to work with multiple base directories
• Tests: Added comprehensive tests for pattern expansion and migration
• Documentation: Updated README with examples and pattern syntax

Example config.json:
{
"document_patterns": [ "./documents", "./notes//*.md", "./projects/backend//*.md" ], ... }

Pattern examples:

• "./documents" - All .md files in directory
• "./docs/**/*.md" - Recursive search with **
• "./projects//docs/.md" - Wildcard patterns
• "/path/to/external/docs" - Absolute paths