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/cli/prune.go

@@ -31,7 +31,7 @@ Snapshot create --prune and snapshot remove run the same cleanup
 automatically; this command is the manual entry point for the same
 work (e.g. after a crashed backup or to reclaim storage).`,
 		Args: cobra.NoArgs,
-		RunE: func(cmd *cobra.Command, args []string) error {
+		RunE: func(cmd *cobra.Command, _ []string) error {
 			// Use unified config resolution
 			configPath, err := ResolveConfigPath()
 			if err != nil {
@@ -43,7 +43,7 @@ work (e.g. after a crashed backup or to reclaim storage).`,
 
 			return RunWithApp(cmd.Context(), AppOptions{
 				ConfigPath: configPath,
-				LogOptions: log.LogOptions{
+				LogOptions: log.Options{
 					Verbose: rootFlags.Verbose,
 					Debug:   rootFlags.Debug,
 					Quiet:   rootFlags.Quiet || opts.JSON,
@@ -52,7 +52,7 @@ work (e.g. after a crashed backup or to reclaim storage).`,
 				Invokes: []fx.Option{
 					fx.Invoke(func(v *vaultik.Vaultik, lc fx.Lifecycle) {
 						lc.Append(fx.Hook{
-							OnStart: func(ctx context.Context) error {
+							OnStart: func(_ context.Context) error {
 								// Start the prune operation in a goroutine
 								go func() {
 									// Run the prune operation
@@ -77,7 +77,7 @@ work (e.g. after a crashed backup or to reclaim storage).`,
 
 								return nil
 							},
-							OnStop: func(ctx context.Context) error {
+							OnStop: func(_ context.Context) error {
 								log.Debug("Stopping prune operation")
 								v.Cancel()