[P2-Enhancement] Add time-decay and source weighting to hybrid search

[VirtualAgentics]

Description

Enhance the hybrid search implementation with time-decay scoring and source weighting to improve search relevance and user experience.

Background

This enhancement extends Issue #58 (hybrid search) by adding sophisticated scoring factors that consider content freshness and source credibility, leading to more relevant search results.

Requirements

• Implement time-decay scoring: score = α·sim + β·bm25 + γ·freshness + δ·source_weight
• Add configurable weights for each scoring factor
• Implement namespace-specific boost factors
• Add source credibility scoring
• Add freshness calculation based on document timestamps
• Make scoring factors configurable via environment variables
• Add unit tests for scoring calculations

Implementation Details

Files to modify:

• src/contextforge_memory/search/ - Extend hybrid search service
• src/contextforge_memory/config.py - Add scoring configuration
• src/contextforge_memory/main.py - Add scoring parameters to search endpoint
• tests/ - Add scoring tests
• README.md - Document scoring parameters

Technical approach:

• Extend existing hybrid search with additional scoring factors
• Add configuration for α, β, γ, δ weights
• Implement time-decay calculation based on document age
• Add source weighting based on namespace or metadata
• Create scoring explanation for debugging

Acceptance Criteria

• Time-decay scoring works correctly with configurable weights
• Source weighting improves result relevance
• All scoring factors are configurable
• Unit tests pass for scoring calculations
• Documentation explains scoring parameters

Testing Requirements

• Unit tests for each scoring factor
• Integration tests for combined scoring
• Performance tests for scoring overhead
• Relevance tests with sample data

Documentation Updates

• README.md - Document scoring parameters
• API documentation - Search scoring options
• Configuration guide - Scoring weights
• Examples - Scoring configuration

Related Issues

• Extends: [P2] Add hybrid search with BM25 + semantic vectors #58 (hybrid search)
• Depends on: None
• Blocks: None