Revamp docs site: new theme, comprehensive landing page, complete nav

Theme:
- Deep purple + amber accent, Inter font, JetBrains Mono for code
- Sticky nav tabs, instant navigation, search sharing, progress bar
- Custom CSS: hero section, feature grid, stats bar, card hover effects
- Mermaid diagram support for architecture visualization

Landing page (index.md) rewrite:
- Stats bar: 87% reduction, 100% accuracy, 6 algorithms, 100+ providers
- Interactive quick-start tabs (proxy, SDK, coding agents, LiteLLM)
- Framework integration grid with code snippets (LangChain, Agno, Strands, MCP)
- Mermaid pipeline diagram showing ContentRouter routing logic
- Content type → compressor mapping table
- Full benchmark results table
- Feature cards linking to deep-dive docs

Navigation reorganized:
- All 29 doc pages now in nav (was 22, 7 orphaned)
- Logical grouping: Getting Started, User Guide, Integrations, How It Works,
  Benchmarks, Reference, Deployment
- Added: SharedContext, Learn, Limitations, Integration Guide overview

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: chopratejas