Update golangci-lint to v2.12.2 with canonical config (#62)

Updates golangci-lint to v2.12.2 everywhere it is pinned and installs the canonical `.golangci.yml`, then remediates every finding the new linter/config surfaces so `make check` is green.

## Version bump

- `Dockerfile` lint stage: `golangci/golangci-lint:v2.11.3-alpine` -> `v2.12.2-alpine` (digest-pinned, date comment updated)
- `Makefile` `deps` target: `go install` moved from the old v1 module path at `@latest` to the pinned `github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2`
- `.golangci.yml` replaced with the canonical config (v2 schema; settings under `linters.settings` so the thresholds actually apply; `default: all` with the standard six disables)
- `script/bootstrap` installs golangci-lint via the system package manager and carries no version pin, so it is unchanged
- CI (`.gitea/workflows/check.yml`) only runs `script/cibuild`, so it needed no change

## Lint remediation

The canonical config surfaced ~3,300 findings across 56k lines. All are fixed, behavior-preserving; incorporates and supersedes the per-package mechanical passes already merged to `main` (refs #61). Highlights:

- `err113`: dynamic errors replaced with package sentinels + `%w` wrapping; comparisons via `errors.Is`
- `goprintffuncname`: printf-style helpers renamed with an `f` suffix (`ui.Writer` message methods, `cli.ReportErrorf`, `database.Fatalf`) and all call sites updated
- `revive` stutter renames: `blob.Handler`, `blob.WithReader`, `blob.ChunkPosition`, `storage.URL`, `storage.Info`; missing doc comments added
- `contextcheck`/`noctx`: `context.Context` threaded through `blob.Packer` and the scanner call sites; context-aware `exec`/`sql` variants
- `funlen`/`cyclop`/`gocognit`/`dupl`: oversized and duplicated functions split into focused helpers (production and test code)
- tests: `t.Parallel()` added where safe (global logger init kept in the serial phase for `-race`), `t.TempDir()`/`t.Helper()` adopted, several suites converted to external test packages
- `gosec`: bounded integer conversions, `ReadHeaderTimeout` on the test HTTP server; remaining warnings suppressed per-site with justifications
- remaining `nolint` directives are rare, targeted, and each carries a reason (e.g. `nilnil` not-found contract in the repository layer, fx module globals, on-disk snake_case struct tags)
- removed the deprecated `log.LogOptions` alias (callers migrated to `log.Options`)

`make check` (tests with `-race`, lint, fmt-check) passes.

Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #62
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/s3/client_test.go

@@ -9,6 +9,7 @@ import (
 	"sneak.berlin/go/vaultik/internal/s3"
 )
 
+//nolint:paralleltest // test servers share a fixed localhost port
 func TestClient(t *testing.T) {
 	ts := NewTestServer(t)
 	defer func() {
@@ -33,11 +34,21 @@ func TestClient(t *testing.T) {
 		t.Fatalf("failed to create client: %v", err)
 	}
 
-	// Test PutObject
 	testKey := "foo/bar.txt"
 	testData := []byte("test data")
 
-	err = client.PutObject(ctx, testKey, bytes.NewReader(testData))
+	verifyPutGetHead(ctx, t, client, testKey, testData)
+	verifyListAndDelete(ctx, t, client, testKey)
+}
+
+// verifyPutGetHead uploads an object, reads it back, and checks existence.
+func verifyPutGetHead(
+	ctx context.Context, t *testing.T, client *s3.Client,
+	testKey string, testData []byte,
+) {
+	t.Helper()
+
+	err := client.PutObject(ctx, testKey, bytes.NewReader(testData))
 	if err != nil {
 		t.Fatalf("failed to put object: %v", err)
 	}
@@ -72,8 +83,15 @@ func TestClient(t *testing.T) {
 	if !exists {
 		t.Error("expected object to exist")
 	}
+}
+
+// verifyListAndDelete lists the object's prefix, deletes it, and checks
+// it is gone.
+func verifyListAndDelete(
+	ctx context.Context, t *testing.T, client *s3.Client, testKey string,
+) {
+	t.Helper()
 
-	// Test ListObjects
 	keys, err := client.ListObjects(ctx, "foo/")
 	if err != nil {
 		t.Fatalf("failed to list objects: %v", err)
@@ -94,7 +112,7 @@ func TestClient(t *testing.T) {
 	}
 
 	// Verify deletion
-	exists, err = client.HeadObject(ctx, testKey)
+	exists, err := client.HeadObject(ctx, testKey)
 	if err != nil {
 		t.Fatalf("failed to head object after deletion: %v", err)
 	}