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/models.go

@@ -1,5 +1,3 @@
-// Package database provides data models and repository interfaces for the Vaultik backup system.
-// It includes types for files, chunks, blobs, snapshots, and their relationships.
 package database
 
 import (
@@ -13,9 +11,12 @@ import (
 // and symlink targets. This information is used to restore files with their
 // original attributes.
 type File struct {
-	ID         types.FileID     // UUID primary key
-	Path       types.FilePath   // Absolute path of the file
-	SourcePath types.SourcePath // The source directory this file came from (for restore path stripping)
+	ID   types.FileID   // UUID primary key
+	Path types.FilePath // Absolute path of the file
+
+	// SourcePath is the source directory this file came from (used for
+	// restore path stripping).
+	SourcePath types.SourcePath
 	MTime      time.Time
 	Size       int64
 	Mode       uint32
@@ -55,13 +56,16 @@ type Chunk struct {
 // The blob creation process is: chunks are accumulated -> compressed with zstd
 // -> encrypted with age -> hashed -> uploaded to S3 with the hash as filename.
 type Blob struct {
-	ID               types.BlobID   // UUID assigned when blob creation starts
-	Hash             types.BlobHash // SHA256 of final compressed+encrypted content (empty until finalized)
-	CreatedTS        time.Time      // When blob creation started
-	FinishedTS       *time.Time     // When blob was finalized (nil if still packing)
-	UncompressedSize int64          // Total size of raw chunks before compression
-	CompressedSize   int64          // Size after compression and encryption
-	UploadedTS       *time.Time     // When blob was uploaded to S3 (nil if not uploaded)
+	ID types.BlobID // UUID assigned when blob creation starts
+
+	// Hash is the SHA256 of the final compressed+encrypted content
+	// (empty until finalized).
+	Hash             types.BlobHash
+	CreatedTS        time.Time  // When blob creation started
+	FinishedTS       *time.Time // When blob was finalized (nil if still packing)
+	UncompressedSize int64      // Total size of raw chunks before compression
+	CompressedSize   int64      // Size after compression and encryption
+	UploadedTS       *time.Time // When blob was uploaded to S3 (nil if not uploaded)
 }
 
 // BlobChunk represents the mapping between blobs and the chunks they contain.
@@ -75,9 +79,10 @@ type BlobChunk struct {
 	Length    int64
 }
 
-// ChunkFile represents the reverse mapping showing which files contain a specific chunk.
-// This is used during deduplication to identify all files that share a chunk,
-// which is important for garbage collection and integrity verification.
+// ChunkFile represents the reverse mapping showing which files contain a
+// specific chunk. This is used during deduplication to identify all files
+// that share a chunk, which is important for garbage collection and
+// integrity verification.
 type ChunkFile struct {
 	ChunkHash  types.ChunkHash
 	FileID     types.FileID
@@ -87,17 +92,20 @@ type ChunkFile struct {
 
 // Snapshot represents a snapshot record in the database
 type Snapshot struct {
-	ID                   types.SnapshotID
-	Hostname             types.Hostname
-	VaultikVersion       types.Version
-	VaultikGitRevision   types.GitRevision
-	StartedAt            time.Time
-	CompletedAt          *time.Time // nil if still in progress
-	FileCount            int64
-	ChunkCount           int64
-	BlobCount            int64
-	TotalSize            int64   // Total size of all referenced files
-	BlobSize             int64   // Total size of all referenced blobs (compressed and encrypted)
+	ID                 types.SnapshotID
+	Hostname           types.Hostname
+	VaultikVersion     types.Version
+	VaultikGitRevision types.GitRevision
+	StartedAt          time.Time
+	CompletedAt        *time.Time // nil if still in progress
+	FileCount          int64
+	ChunkCount         int64
+	BlobCount          int64
+	TotalSize          int64 // Total size of all referenced files
+
+	// BlobSize is the total size of all referenced blobs (compressed and
+	// encrypted).
+	BlobSize             int64
 	BlobUncompressedSize int64   // Total uncompressed size of all referenced blobs
 	CompressionRatio     float64 // Compression ratio (BlobSize / BlobUncompressedSize)
 	CompressionLevel     int     // Compression level used for this snapshot