Remediate all lint findings under the canonical golangci-lint config

Fix every finding surfaced by the canonical .golangci.yml with
golangci-lint v2.12.2 (refs #61), behavior-preserving throughout:

- err113: dynamic errors replaced with package-level sentinels and %w
  wrapping; direct comparisons converted to errors.Is
- goprintffuncname: printf-style helpers renamed with an f suffix
  (ui.Writer message methods, cli.ReportErrorf, database.Fatalf,
  vaultik stdoutf) and all call sites updated
- revive: stuttering type names renamed (blob.Handler, blob.WithReader,
  blob.ChunkPosition, storage.URL, storage.Info), doc comments added,
  unused parameters blanked, package comments added
- contextcheck/noctx: ctx threaded through blob.Packer
  (AddChunk/Flush/FinalizeBlob/PackChunks) and scanner call sites;
  context-aware exec and sql variants used
- funlen/cyclop/gocognit/nestif/dupl: oversized or duplicated
  functions split into focused helpers across production and test code
- paralleltest/tparallel/thelper/usetesting/testpackage: tests
  parallelized where safe (global log.Initialize kept in the serial
  phase), helpers marked, t.TempDir adopted, external test packages
  where only exported API is used
- gosec: integer conversions clamped or justified, header timeouts
  added, remaining findings suppressed with per-site justifications
- mnd/goconst/lll/wsl_v5/nlreturn/noinlineerr/errcheck and other
  mechanical findings fixed directly

Remove the deprecated log.LogOptions alias (callers migrated to
log.Options). make check is green.

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)