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/snapshot/module.go

@@ -21,6 +21,8 @@ type ScannerParams struct {
 // Module exports backup functionality as an fx module.
 // It provides a ScannerFactory that can create Scanner instances
 // with custom parameters while sharing common dependencies.
+//
+//nolint:gochecknoglobals // fx module definitions are conventionally globals
 var Module = fx.Module("backup",
 	fx.Provide(
 		provideScannerFactory,
@@ -31,7 +33,9 @@ var Module = fx.Module("backup",
 // ScannerFactory creates scanners with custom parameters
 type ScannerFactory func(params ScannerParams) *Scanner
 
-func provideScannerFactory(cfg *config.Config, repos *database.Repositories, storer storage.Storer) ScannerFactory {
+func provideScannerFactory(
+	cfg *config.Config, repos *database.Repositories, storer storage.Storer,
+) ScannerFactory {
 	return func(params ScannerParams) *Scanner {
 		// Use provided excludes, or fall back to global config excludes
 		excludes := params.Exclude