Resolves #8 - Configuration documentation and scheduler interaction

BREAKING CHANGE: Configuration logic redesigned for better user experience

The extension previously had confusing dual configuration between Scheduler
and TypoScript with unclear precedence and documentation gaps. This update
unifies everything into a single, well-documented qualityLevel parameter.

New features:
- Single qualityLevel parameter replaces minimumSimilarity/proximityThreshold split
- Automatic storage optimization (qualityLevel - 0.1)
- Unified exclusion handling across Scheduler and TypoScript
- Automatic migration from legacy configurations
- Simplified Scheduler interface with clear explanations
- Comprehensive documentation with practical examples

Benefits:
- Eliminates configuration hierarchy confusion reported in #8
- Prevents impossible configurations (proximityThreshold < minimumSimilarity)
- Reduces support requests and user errors
- Self-documenting configuration values
- Maintains full backward compatibility

Technical changes:
- GenerateSimilaritiesTask: Add qualityLevel with migration logic
- AdditionalFieldProvider: Simplified unified interface with help text
- SuggestionService: Unified quality level resolution
- TypoScript: New qualityLevel constants with legacy support
- Documentation: Complete rewrite addressing configuration confusion

Migration: Existing configurations automatically migrate on first use
Recommended values: 0.25 (German), 0.30 (standard), 0.35+ (selective)

Closes #8