feat(nightwatch): add dual-panel evaluation for drift detection

Add DualPanelResult struct and dual_panel_evaluate function to enable
two independent quality assessments on agent output. Drift is detected
when panel agreement falls below 0.5.

Panel A: Scores based on ReasoningCertificate quality (premises,
claims, edge cases, confidence)
Panel B: Scores based on output structure (sections, evidence markers,
conclusion markers, minimum length)

Includes comprehensive unit tests covering:
- Both panels agree (no drift)
- Panels disagree (drift detected)
- Missing certificate scenario

Refs #91

Author: AlexMikhalev

crates/terraphim_orchestrator/src/lib.rs

@@ -55,8 +55,9 @@ pub use error::OrchestratorError;
 pub use handoff::{HandoffBuffer, HandoffContext, HandoffLedger};
 pub use mode::{IssueMode, TimeMode};
 pub use nightwatch::{
-    validate_certificate, Claim, CorrectionAction, CorrectionLevel, DriftAlert, DriftMetrics,
-    DriftScore, NightwatchMonitor, RateLimitTracker, RateLimitWindow, ReasoningCertificate,
+    dual_panel_evaluate, validate_certificate, Claim, CorrectionAction, CorrectionLevel,
+    DriftAlert, DriftMetrics, DriftScore, DualPanelResult, NightwatchMonitor, RateLimitTracker,
+    RateLimitWindow, ReasoningCertificate,
 };
 pub use persona::{MetapromptRenderError, MetapromptRenderer, PersonaRegistry};
 pub use scheduler::{ScheduleEvent, TimeScheduler};