Update golangci-lint to v2.12.2 with canonical config (#187)

Bumps golangci-lint from v2.10.1 to v2.12.2 everywhere it is pinned and installs the canonical `.golangci.yml`, then fixes every finding the new linter surfaces so `make check` is green.

## Version pins

- `Dockerfile` lint stage: `golangci/golangci-lint:v2.12.2` (Debian-based), tag plus digest pin
- `script/bootstrap`: `GOLANGCI_LINT_VERSION=2.12.2` with updated `linux-amd64`/`linux-arm64` release-archive sha256 pins

## Config

`.golangci.yml` replaced with the canonical config. Material change: the old file declared `version: "2"` but kept settings under the legacy top-level `linters-settings` key, which golangci-lint v2 ignores — so the intended thresholds (`lll` 88, `funlen` 80/50, `cyclop` 15, `dupl` 100) were not being applied. The canonical file moves them under `linters.settings` and drops `issues.exclude-use-default`.

## Lint fixes (216 findings)

- `lll` (96): wrapped lines to the 88-column limit
- `noctx` (46): `httptest.NewRequestWithContext` with `t.Context()` throughout the tests
- `goconst` (24): shared constants for template/JSON keys in `internal/handlers` and repeated test literals
- `gosec` (23): app-page redirects now go through a `redirectToApp` helper that path-escapes the app ID (G710 open redirect); `http.ServeFile` of the internally derived deployment log path annotated like the adjacent `os.Stat` (G703)
- `dupl` (22): extracted a generic `findAllByAppID` in `internal/models`, a `deleteAppResource` helper in `internal/handlers`, a shared `parsePush` in `internal/service/webhook`, and table-driven/helper-based dedup in tests
- `nolintlint` (5): removed `//nolint:funlen` directives made obsolete by the new limits (plus one more that became obsolete after refactoring)
- `nilerr` (3, surfaced during fixing): resource-delete lookups now propagate the find error to the caller

No behavior changes intended; all tests pass and `make check` is green.

Note: golangci-lint v2.12 warns that `gomodguard` is deprecated in favor of `gomodguard_v2` — a future canonical-config update should address this centrally.
Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #187
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/models/label.go

@@ -93,6 +93,10 @@ func FindLabel(
 	return label, nil
 }
 
+func (l *Label) scanDest() []any {
+	return []any{&l.ID, &l.AppID, &l.Key, &l.Value}
+}
+
 // FindLabelsByAppID finds all labels for an app.
 func FindLabelsByAppID(
 	ctx context.Context,
@@ -103,27 +107,7 @@ func FindLabelsByAppID(
 		SELECT id, app_id, key, value FROM app_labels
 		WHERE app_id = ? ORDER BY key`
 
-	rows, err := db.Query(ctx, query, appID)
-	if err != nil {
-		return nil, fmt.Errorf("querying labels by app: %w", err)
-	}
-
-	defer func() { _ = rows.Close() }()
-
-	var labels []*Label
-
-	for rows.Next() {
-		label := NewLabel(db)
-
-		scanErr := rows.Scan(&label.ID, &label.AppID, &label.Key, &label.Value)
-		if scanErr != nil {
-			return nil, scanErr
-		}
-
-		labels = append(labels, label)
-	}
-
-	return labels, rows.Err()
+	return findAllByAppID(ctx, db, query, appID, "labels", NewLabel)
 }
 
 // DeleteLabelsByAppID deletes all labels for an app.