step 2: Add UUID columns with backfill and dual-write support

- Add migration 000007: Add UUID columns to soundtrack and song with backfill
- Update InsertSoundtrack and InsertSoundtrackWithExistingId to accept UUID
- Update AddSong to accept UUID
- Add dual-write: Go code now generates UUIDs for new records
- Add uuid and pgtype imports

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/db/repository/soundtrack.sql.go

@@ -7,6 +7,8 @@ package repository
 
 import (
 	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
 )
 
 const addSoundtrackPlayed = `-- name: AddSoundtrackPlayed :exec
@@ -153,36 +155,44 @@ func (q *Queries) GetSoundtrackNameById(ctx context.Context, id int32) (string,
 }
 
 const insertSoundtrack = `-- name: InsertSoundtrack :one
-INSERT INTO soundtrack (soundtrack_name, path, hash, added) VALUES ($1, $2, $3, now()) returning id
+INSERT INTO soundtrack (uuid, soundtrack_name, path, hash, added) VALUES ($1, $2, $3, $4, now()) returning id
 `
 
 type InsertSoundtrackParams struct {
-	SoundtrackName string `json:"soundtrack_name"`
-	Path           string `json:"path"`
-	Hash           string `json:"hash"`
+	Uuid           pgtype.UUID `json:"uuid"`
+	SoundtrackName string      `json:"soundtrack_name"`
+	Path           string      `json:"path"`
+	Hash           string      `json:"hash"`
 }
 
 func (q *Queries) InsertSoundtrack(ctx context.Context, arg InsertSoundtrackParams) (int32, error) {
-	row := q.db.QueryRow(ctx, insertSoundtrack, arg.SoundtrackName, arg.Path, arg.Hash)
+	row := q.db.QueryRow(ctx, insertSoundtrack,
+		arg.Uuid,
+		arg.SoundtrackName,
+		arg.Path,
+		arg.Hash,
+	)
 	var id int32
 	err := row.Scan(&id)
 	return id, err
 }
 
 const insertSoundtrackWithExistingId = `-- name: InsertSoundtrackWithExistingId :exec
-INSERT INTO soundtrack (id, soundtrack_name, path, hash, added) VALUES ($1, $2, $3, $4, now())
+INSERT INTO soundtrack (id, uuid, soundtrack_name, path, hash, added) VALUES ($1, $2, $3, $4, $5, now())
 `
 
 type InsertSoundtrackWithExistingIdParams struct {
-	ID             int32  `json:"id"`
-	SoundtrackName string `json:"soundtrack_name"`
-	Path           string `json:"path"`
-	Hash           string `json:"hash"`
+	ID             int32       `json:"id"`
+	Uuid           pgtype.UUID `json:"uuid"`
+	SoundtrackName string      `json:"soundtrack_name"`
+	Path           string      `json:"path"`
+	Hash           string      `json:"hash"`
 }
 
 func (q *Queries) InsertSoundtrackWithExistingId(ctx context.Context, arg InsertSoundtrackWithExistingIdParams) error {
 	_, err := q.db.Exec(ctx, insertSoundtrackWithExistingId,
 		arg.ID,
+		arg.Uuid,
 		arg.SoundtrackName,
 		arg.Path,
 		arg.Hash,