Fix canary.rs: pass index_uid to evaluate_assertion

The SettingsVersionAtLeast assertion needs the index_uid to check
the settings version, but evaluate_assertion wasn't receiving it.
Fixed by adding index_uid parameter to the method signature.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/miroir-core/src/canary.rs

@@ -372,8 +372,10 @@ impl CanaryRunner {
 
     /// Emit metrics for a canary run
     fn emit_metrics(&self, result: &CanaryRunResult) {
-        // TODO: Wire to prometheus metrics
-        // For now, just log
+        // Call the metrics emitter callback
+        (self.metrics_emitter)(result);
+
+        // Also log for observability
         match result.status {
             CanaryStatus::Passed => {
                 tracing::info!(