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/database/module.go

@@ -11,7 +11,13 @@ import (
 	"sneak.berlin/go/vaultik/internal/log"
 )
 
+// indexDirPerm restricts the local index directory to the owning user;
+// the index describes the backed-up file tree and must stay private.
+const indexDirPerm = 0o700
+
 // Module provides database dependencies
+//
+//nolint:gochecknoglobals // fx module definitions are package globals by convention
 var Module = fx.Module("database",
 	fx.Provide(
 		provideDatabase,
@@ -22,7 +28,9 @@ var Module = fx.Module("database",
 func provideDatabase(lc fx.Lifecycle, cfg *config.Config) (*DB, error) {
 	// Ensure the index directory exists
 	indexDir := filepath.Dir(cfg.IndexPath)
-	if err := os.MkdirAll(indexDir, 0700); err != nil {
+
+	err := os.MkdirAll(indexDir, indexDirPerm)
+	if err != nil {
 		return nil, fmt.Errorf("creating index directory: %w", err)
 	}
 
@@ -32,7 +40,7 @@ func provideDatabase(lc fx.Lifecycle, cfg *config.Config) (*DB, error) {
 	}
 
 	lc.Append(fx.Hook{
-		OnStop: func(ctx context.Context) error {
+		OnStop: func(_ context.Context) error {
 			log.Debug("Database module OnStop hook called")
 
 			err := db.Close()