Update golangci-lint to v2.12.2 with canonical config

Bump golangci-lint from v2.10.1 to v2.12.2 in the Dockerfile lint
stage (tag+digest pin) and script/bootstrap release-archive pins
(linux amd64/arm64 sha256s). Replace .golangci.yml with the canonical
v2-layout config so linter settings (lll 88, funlen 80/50, cyclop 15,
dupl 100) actually apply.

Fix all findings surfaced by the new linter and config:

- noctx: use httptest.NewRequestWithContext in all tests
- gosec G710/G703: route app redirects through a path-escaping
  redirectToApp helper; annotate internal log path usage
- goconst: introduce shared constants for template/JSON keys and
  repeated test literals
- lll: wrap lines to the 88-column limit
- dupl: extract shared helpers (generic findAllByAppID in models,
  deleteAppResource in handlers, parsePush in webhook payloads,
  table-driven/helper-based test dedup)
- nolintlint: drop nolint directives made obsolete by the new limits

Record the change in TODO.md; make check is green.

internal/models/volume.go

@@ -103,6 +103,12 @@ func FindVolume(
 	return vol, nil
 }
 
+func (v *Volume) scanDest() []any {
+	return []any{
+		&v.ID, &v.AppID, &v.HostPath, &v.ContainerPath, &v.ReadOnly,
+	}
+}
+
 // FindVolumesByAppID finds all volumes for an app.
 func FindVolumesByAppID(
 	ctx context.Context,
@@ -113,30 +119,7 @@ func FindVolumesByAppID(
 		SELECT id, app_id, host_path, container_path, readonly
 		FROM app_volumes WHERE app_id = ? ORDER BY container_path`
 
-	rows, err := db.Query(ctx, query, appID)
-	if err != nil {
-		return nil, fmt.Errorf("querying volumes by app: %w", err)
-	}
-
-	defer func() { _ = rows.Close() }()
-
-	var volumes []*Volume
-
-	for rows.Next() {
-		vol := NewVolume(db)
-
-		scanErr := rows.Scan(
-			&vol.ID, &vol.AppID, &vol.HostPath,
-			&vol.ContainerPath, &vol.ReadOnly,
-		)
-		if scanErr != nil {
-			return nil, scanErr
-		}
-
-		volumes = append(volumes, vol)
-	}
-
-	return volumes, rows.Err()
+	return findAllByAppID(ctx, db, query, appID, "volumes", NewVolume)
 }
 
 // DeleteVolumesByAppID deletes all volumes for an app.