Eliminate all compiler warnings (79 Γזע 0)

- Remove unused mach vm_prot_t type and VM_PROT_* constants
- Remove unused EmailChannel.smtp_config field
- Remove unused AttributionEngine.campaigns field
- Remove unused BehaviorSignature.confidence_threshold field
- Prefix unused DetectionEngine._config with underscore
- Prefix unused MitreAttackEngine._campaigns with underscore
- Prefix unused NeuralMemoryAnalyzer._confidence_threshold with underscore

All tests passing (24 total). Clean build with zero warnings.

ghost-core/src/detection.rs

@@ -66,7 +66,7 @@ pub struct DetectionEngine {
     threat_intelligence: ThreatIntelligence,
     evasion_detector: EvasionDetector,
     mitre_engine: MitreAttackEngine,
-    config: Option<DetectionConfig>,
+    _config: Option<DetectionConfig>,
     #[cfg(target_os = "linux")]
     ebpf_detector: Option<EbpfDetector>,
 }
@@ -130,7 +130,7 @@ impl DetectionEngine {
             threat_intelligence,
             evasion_detector,
             mitre_engine,
-            config,
+            _config: config,
             #[cfg(target_os = "linux")]
             ebpf_detector,
         })