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/chunker/chunker_isolated_test.go

@@ -1,11 +1,15 @@
-package chunker
+package chunker_test
 
 import (
 	"bytes"
 	"testing"
+
+	"sneak.berlin/go/vaultik/internal/chunker"
 )
 
 func TestChunkerExpectedChunkCount(t *testing.T) {
+	t.Parallel()
+
 	tests := []struct {
 		name         string
 		fileSize     int
@@ -38,16 +42,19 @@ func TestChunkerExpectedChunkCount(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			chunker := NewChunker(tt.avgChunkSize)
+			t.Parallel()
+
+			c := chunker.NewChunker(tt.avgChunkSize)
 
 			// Create data with some variation to trigger chunk boundaries
 			data := make([]byte, tt.fileSize)
 			for i := range data {
 				// Use a pattern that should create boundaries
+				//nolint:gosec // G115: intentional byte truncation
 				data[i] = byte((i * 17) ^ (i >> 5))
 			}
 
-			chunks, err := chunker.ChunkReader(bytes.NewReader(data))
+			chunks, err := c.ChunkReader(bytes.NewReader(data))
 			if err != nil {
 				t.Fatalf("chunking failed: %v", err)
 			}