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/entry.go

@@ -9,15 +9,19 @@ import (
 	"sneak.berlin/go/vaultik/internal/ui"
 )
 
-// CLIEntry is the main entry point for the CLI application.
+// shortCommitLen is the number of git commit hash characters shown in
+// the startup banner.
+const shortCommitLen = 12
+
+// Entry is the main entry point for the CLI application.
 // It prints the startup banner (unless a quiet flag is present in os.Args),
 // executes the root cobra command, and routes any returned error through
 // the ui.Writer so the user sees a properly formatted "🛑 ERROR:" line.
-func CLIEntry() {
+func Entry() {
 	if !bannerSuppressedInArgs(os.Args[1:]) {
 		short := globals.Commit
-		if len(short) > 12 {
-			short = short[:12]
+		if len(short) > shortCommitLen {
+			short = short[:shortCommitLen]
 		}
 
 		writeStartupBanner(ui.New(os.Stdout), time.Now().UTC(), short)