refactor: consolidate applyMigrations into single exported function

Remove the unexported applyMigrations() and the runMigrations() method.
ApplyMigrations() is now the single implementation, accepting context
and an optional logger. connect() calls it directly.

All callers updated to pass context.Background() and nil logger.

internal/handlers/handlers_test.go

@@ -82,7 +82,7 @@ func setupTestDB(t *testing.T) *sql.DB {
 		t.Fatalf("failed to open test db: %v", err)
 	}
 
-	if err := database.ApplyMigrations(db); err != nil {
+	if err := database.ApplyMigrations(context.Background(), db, nil); err != nil {
 		t.Fatalf("failed to apply migrations: %v", err)
 	}