Document the confidence scoring algorithm

[rajkumarsakthivel]

Add documentation explaining how CCE's confidence scorer works.

Why: The README mentions "a confidence scorer blends similarity (50%), keyword match (30%), and recency (20%)" but there's no deeper explanation for users who want to understand or tune retrieval quality.

Steps:

1. Read the scorer implementation in src/context_engine/
2. Document the algorithm in docs/wiki/Confidence-Scoring.md
3. Cover: inputs, weight formula, how scores map to results ordering, and how confidence_threshold config works
4. Add a link from the existing How It Works wiki page

Keep it concise. A diagram or formula would be helpful but not required.

[ahfoysal]

I documented the confidence scoring path and threshold tuning in PR 126. It adds a dedicated confidence scoring wiki page and links it from the How It Works section.