Integrate YARA engine into detection pipeline

- Added YARA engine to DetectionEngine struct
- Initialize YARA with default rules directory on engine creation
- Integrated YARA memory scanning into analyze_process method
- Map YARA threat levels to confidence scores
- Log YARA matches with rule names and memory offsets
- Handle async YARA scanning in sync detection context

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

ghost-core/src/lib.rs

@@ -110,5 +110,6 @@ pub use threat_intel::{
     ThreatContext, ThreatIntelligence,
 };
 pub use yara_engine::{
-    DynamicYaraEngine, RuleMatch, ThreatLevel as YaraThreatLevel, YaraRuleSource, YaraScanResult,
+    DynamicYaraEngine, RuleMatch, ThreatLevel as YaraThreatLevel, YaraRuleMetadata,
+    YaraScanResult,
 };