iOS Skills System Implementation

This document describes the complete iOS implementation of the TrajectoryOS Skills System, achieving full parity with the Tauri desktop version while leveraging native Apple technologies. **Features:** - Configurable half-life per skill (default: 90 days) - Decay floor (never drops below minimum) - Evergreen skills (no decay) - Recovery rate when practicing **Relationship Types:** - `prerequisite` - Skill A must be learned before B - `synergy` - Skills enhance each other - `variant` - Skills are variations - `enhances` - Skill A makes B more effective **Graph Operations:** - Build complete skill graph - Find prerequisites/dependents - Topological sort for learning order - Calculate skill transfer **Target Management:** - Define skill targets (e.g., "Senior iOS Developer") - Set required skills with levels - Track progress toward targets