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/queries/song.sql

@@ -5,7 +5,7 @@ DELETE FROM song;
 DELETE FROM song WHERE soundtrack_id = $1;
 
 -- name: AddSong :exec
-INSERT INTO song(soundtrack_id, song_name, path, file_name, hash) VALUES ($1, $2, $3, $4, $5);
+INSERT INTO song(uuid, soundtrack_id, song_name, path, file_name, hash) VALUES ($1, $2, $3, $4, $5, $6);
 
 -- name: CheckSong :one
 SELECT COUNT(*) FROM song WHERE soundtrack_id = $1 AND path = $2;

internal/db/queries/soundtrack.sql

@@ -29,10 +29,10 @@ UPDATE soundtrack SET deleted=NULL WHERE id=$1;
 SELECT id FROM soundtrack WHERE soundtrack_name = $1;
 
 -- 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;
 
 -- 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());
 
 -- name: FindAllSoundtracks :many
 SELECT *