feat(uploads): choose the language of a recording; record it, show it, carry it to the engines (#61)

Form field (Swedish preselected, Other = auto) read before the file part and refused
before anything is spooled if outside the closed set; stored on the row (migration 021,
CHECK constraint, default sv for history); carried on the Job and the worker's context;
shown on the status page. Feature scenarios and the coverage map are updated, and
ADR-033/034 amended.

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

internal/domain/domain.go

@@ -243,9 +243,12 @@ const (
 // never stored in, or merged with, the shared public-caption Transcript (ADR-021).
 // Content and Segments are empty until Status is UploadDone.
 type UploadedTranscript struct {
-	ID           string
-	UserID       string
-	Title        string
+	ID     string
+	UserID string
+	Title  string
+	// Language is what the upload was (or will be) transcribed as: sv, or auto for
+	// "Other" (tapir#61).
+	Language     Language
 	Status       UploadStatus
 	Content      string
 	Segments     []Segment