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/models/models_test.go

@@ -1,17 +1,21 @@
-package models
+package models_test
 
 import (
 	"testing"
 	"time"
+
+	"sneak.berlin/go/vaultik/internal/models"
 )
 
 // TestModelsCompilation ensures all model types can be instantiated
 func TestModelsCompilation(t *testing.T) {
+	t.Parallel()
+
 	// This test primarily serves as a compilation test
 	// to ensure all types are properly defined
 
 	// Test FileInfo
-	fi := &FileInfo{
+	fi := &models.FileInfo{
 		Path:  "/test/file.txt",
 		MTime: time.Now(),
 		Size:  1024,
@@ -21,7 +25,7 @@ func TestModelsCompilation(t *testing.T) {
 	}
 
 	// Test ChunkInfo
-	ci := &ChunkInfo{
+	ci := &models.ChunkInfo{
 		Hash:   "abc123",
 		Size:   512,
 		Offset: 0,
@@ -31,7 +35,7 @@ func TestModelsCompilation(t *testing.T) {
 	}
 
 	// Test BlobInfo
-	bi := &BlobInfo{
+	bi := &models.BlobInfo{
 		Hash:       "blob123",
 		CreatedAt:  time.Now(),
 		Size:       1024,
@@ -42,7 +46,7 @@ func TestModelsCompilation(t *testing.T) {
 	}
 
 	// Test Snapshot
-	s := &Snapshot{
+	s := &models.Snapshot{
 		ID:        "2024-01-01T00:00:00Z",
 		Hostname:  "test-host",
 		Version:   "1.0.0",