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/blobgen/writer_test.go

@@ -1,4 +1,4 @@
-package blobgen
+package blobgen_test
 
 import (
 	"bytes"
@@ -9,12 +9,15 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/vaultik/internal/blobgen"
 )
 
 // TestWriterHashIsDoubleHash verifies that Writer.Sum256() returns
 // the double hash SHA256(SHA256(plaintext)) for security.
 // Double hashing prevents attackers from confirming existence of known content.
 func TestWriterHashIsDoubleHash(t *testing.T) {
+	t.Parallel()
+
 	// Test data - random data that doesn't compress well
 	testData := make([]byte, 1024*1024) // 1MB
 	_, err := rand.Read(testData)
@@ -27,7 +30,7 @@ func TestWriterHashIsDoubleHash(t *testing.T) {
 	var encryptedBuf bytes.Buffer
 
 	// Create blobgen writer
-	writer, err := NewWriter(&encryptedBuf, 3, []string{testRecipient})
+	writer, err := blobgen.NewWriter(&encryptedBuf, 3, []string{testRecipient})
 	require.NoError(t, err)
 
 	// Write test data
@@ -67,6 +70,8 @@ func TestWriterHashIsDoubleHash(t *testing.T) {
 // TestWriterDeterministicHash verifies that the same input always produces
 // the same hash, even with non-deterministic encryption.
 func TestWriterDeterministicHash(t *testing.T) {
+	t.Parallel()
+
 	// Test data
 	testData := []byte("Hello, World! This is test data for deterministic hashing.")
 
@@ -76,13 +81,13 @@ func TestWriterDeterministicHash(t *testing.T) {
 	// Create two writers and verify they produce the same hash
 	var buf1, buf2 bytes.Buffer
 
-	writer1, err := NewWriter(&buf1, 3, []string{testRecipient})
+	writer1, err := blobgen.NewWriter(&buf1, 3, []string{testRecipient})
 	require.NoError(t, err)
 	_, err = writer1.Write(testData)
 	require.NoError(t, err)
 	require.NoError(t, writer1.Close())
 
-	writer2, err := NewWriter(&buf2, 3, []string{testRecipient})
+	writer2, err := blobgen.NewWriter(&buf2, 3, []string{testRecipient})
 	require.NoError(t, err)
 	_, err = writer2.Write(testData)
 	require.NoError(t, err)