Add Agent Sentiment Analyzer - interactive conversation sentiment analysis tool

New interactive page (sentiment-analyzer.html) that analyzes agent conversation
logs for sentiment patterns, emotional drift, and communication health.

Features:
- Rule-based NLP with 50+ positive/negative keywords, intensifiers, negation, emoji
- Animated SVG gauge showing overall sentiment (-1 to +1)
- Communication health score (0-100) with stability/trajectory/positivity factors
- Emotion detection (joy, frustration, confusion, gratitude, urgency)
- Canvas trend chart showing per-message sentiment over time
- Emotional drift alerts when sentiment shifts dramatically
- Per-message timeline with color-coded sentiment bars
- Proactive insights: turning points, pattern analysis, trajectory detection
- 3 preset conversations (Happy Customer, Escalating Frustration, Recovery Arc)
- Dark/light theme toggle
- Responsive design

Usage: Open sentiment-analyzer.html, paste a conversation or try a preset, click Analyze.

Author: sauravbhattacharya001