Implement Category Deduplication System

[Davz33]

Priority: High

Implement automatic category deduplication to prevent redundant categories:

Current Issues:

• Multiple categories with identical or very similar content
• No mechanism to detect and merge duplicate categories
• Manual cleanup required after each categorization

Expected Outcome:

• Automatic detection of duplicate/similar categories
• Intelligent merging of redundant categories
• Clean, distinct category set after each recategorization

Technical Approach:

• Implement category similarity calculation using TF-IDF vectors
• Add deduplication logic in _generate_category_names()
• Merge categories above similarity threshold (e.g., 0.8)
• Preserve the most descriptive category name when merging