docs: Add comprehensive DG_MAX_RATIO tuning guide

Created extensive documentation for the DG_MAX_RATIO parameter, which
controls delta compression efficiency thresholds.

New Documentation:
- docs/DG_MAX_RATIO.md (526 lines)
  * Complete explanation of how DG_MAX_RATIO works
  * Real-world scenarios and use cases
  * Decision trees for choosing optimal values
  * Industry-specific recommendations
  * Monitoring and tuning strategies
  * Advanced usage patterns
  * Comprehensive FAQ

Updates to Existing Documentation:
- README.md: Added link to DG_MAX_RATIO guide with tip callout
- CLAUDE.md: Added detailed DG_MAX_RATIO explanation and guide link
- Dockerfile: Added inline comments explaining DG_MAX_RATIO tuning
- docs/sdk/getting-started.md: Added DG_MAX_RATIO guide reference

Key Topics Covered:
- What DG_MAX_RATIO does and why it exists
- How to choose the right value (0.2-0.7 range)
- Real-world scenarios (nightly builds, major versions, etc.)
- Industry-specific use cases (SaaS, mobile apps, backups, etc.)
- Configuration examples (Docker, SDK, CLI)
- Monitoring and optimization strategies
- Advanced usage patterns (dynamic ratios, A/B testing)
- FAQ addressing common questions

Examples Included:
- Conservative (0.2-0.3): For dissimilar files or expensive storage
- Default (0.5): Balanced approach for most use cases
- Permissive (0.6-0.7): For very similar files or cheap storage

Value Proposition:
- Helps users optimize compression for their specific use case
- Prevents inefficient delta compression
- Provides data-driven tuning methodology
- Reduces support questions about compression behavior

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CLAUDE.md

@@ -189,7 +189,11 @@ Core delta logic is in `src/deltaglider/core/service.py`:
 ## Environment Variables
 
 - `DG_LOG_LEVEL`: Logging level (default: "INFO")
-- `DG_MAX_RATIO`: Maximum acceptable delta/file ratio (default: "0.5")
+- `DG_MAX_RATIO`: Maximum acceptable delta/file ratio (default: "0.5", range: "0.0-1.0")
+  - **See [docs/DG_MAX_RATIO.md](docs/DG_MAX_RATIO.md) for complete tuning guide**
+  - Controls when to use delta vs. direct storage
+  - Lower (0.2-0.3) = conservative, only high-quality compression
+  - Higher (0.6-0.7) = permissive, accept modest savings
 - `DG_CACHE_BACKEND`: Cache backend type - "filesystem" (default) or "memory"
 - `DG_CACHE_MEMORY_SIZE_MB`: Memory cache size limit in MB (default: "100")
 - `DG_CACHE_ENCRYPTION_KEY`: Optional base64-encoded Fernet key for persistent encryption (ephemeral by default)