feat(store): persist and read back the reconciliation

CompleteUpload writes it (SQL NULL when there was none, never the JSON text 'null':
the page claims a second opinion only if the column is non-NULL); GetUpload reads it,
List does not. Mutation-checked.

domain.go and the store are one commit: the store tests need the new field.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/domain/domain.go

@@ -214,7 +214,10 @@ type UploadedTranscript struct {
 	// HadVideo records that the uploaded file carried a video track. Only its audio
 	// was used and the video was discarded; the page says so. It is set at upload
 	// and never cleared (ADR-033).
-	HadVideo   bool
-	CreatedAt  time.Time
-	FinishedAt time.Time // zero until the job reaches done or failed
+	HadVideo bool
+	// Reconciliation is how a merged transcript came about, or nil for a single
+	// engine (ADR-034). Set by Get, not by List.
+	Reconciliation *Reconciliation
+	CreatedAt      time.Time
+	FinishedAt     time.Time // zero until the job reaches done or failed
 }