Update golangci-lint to v2.12.2 with canonical config (#62)

Updates golangci-lint to v2.12.2 everywhere it is pinned and installs the canonical `.golangci.yml`, then remediates every finding the new linter/config surfaces so `make check` is green.

## Version bump

- `Dockerfile` lint stage: `golangci/golangci-lint:v2.11.3-alpine` -> `v2.12.2-alpine` (digest-pinned, date comment updated)
- `Makefile` `deps` target: `go install` moved from the old v1 module path at `@latest` to the pinned `github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2`
- `.golangci.yml` replaced with the canonical config (v2 schema; settings under `linters.settings` so the thresholds actually apply; `default: all` with the standard six disables)
- `script/bootstrap` installs golangci-lint via the system package manager and carries no version pin, so it is unchanged
- CI (`.gitea/workflows/check.yml`) only runs `script/cibuild`, so it needed no change

## Lint remediation

The canonical config surfaced ~3,300 findings across 56k lines. All are fixed, behavior-preserving; incorporates and supersedes the per-package mechanical passes already merged to `main` (refs #61). Highlights:

- `err113`: dynamic errors replaced with package sentinels + `%w` wrapping; comparisons via `errors.Is`
- `goprintffuncname`: printf-style helpers renamed with an `f` suffix (`ui.Writer` message methods, `cli.ReportErrorf`, `database.Fatalf`) and all call sites updated
- `revive` stutter renames: `blob.Handler`, `blob.WithReader`, `blob.ChunkPosition`, `storage.URL`, `storage.Info`; missing doc comments added
- `contextcheck`/`noctx`: `context.Context` threaded through `blob.Packer` and the scanner call sites; context-aware `exec`/`sql` variants
- `funlen`/`cyclop`/`gocognit`/`dupl`: oversized and duplicated functions split into focused helpers (production and test code)
- tests: `t.Parallel()` added where safe (global logger init kept in the serial phase for `-race`), `t.TempDir()`/`t.Helper()` adopted, several suites converted to external test packages
- `gosec`: bounded integer conversions, `ReadHeaderTimeout` on the test HTTP server; remaining warnings suppressed per-site with justifications
- remaining `nolint` directives are rare, targeted, and each carries a reason (e.g. `nilnil` not-found contract in the repository layer, fx module globals, on-disk snake_case struct tags)
- removed the deprecated `log.LogOptions` alias (callers migrated to `log.Options`)

`make check` (tests with `-race`, lint, fmt-check) passes.

Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #62
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/vaultik/helpers.go

@@ -8,13 +8,56 @@ import (
 	"strings"
 	"time"
 
+	"github.com/dustin/go-humanize"
 	"sneak.berlin/go/vaultik/internal/types"
 )
 
+// percentScale converts a 0..1 ratio into a percentage.
+const percentScale = 100
+
+// progressLogEvery is how many processed items pass between progress
+// log lines in long-running loops.
+const progressLogEvery = 100
+
+// ubytes renders a byte count with humanize.Bytes, clamping negative
+// values to zero so the int64→uint64 conversion cannot overflow.
+func ubytes(n int64) string {
+	if n < 0 {
+		n = 0
+	}
+
+	return humanize.Bytes(uint64(n))
+}
+
+// Sentinel errors for snapshot ID and duration parsing.
+var (
+	errMalformedSnapshotID = errors.New(
+		"invalid snapshot ID format: expected hostname_snapshotname_timestamp")
+	errInvalidDuration = errors.New("invalid duration")
+	errUnknownTimeUnit = errors.New("unknown time unit")
+)
+
+// Time-unit lengths used by parseDuration.
+const (
+	day   = 24 * time.Hour
+	week  = 7 * day
+	month = 30 * day
+	year  = 365 * day
+)
+
+// Snapshot IDs split on "_" into hostname, optional name parts, and a
+// trailing timestamp.
+const (
+	minSnapshotIDParts     = 2
+	minSnapshotIDNameParts = 3
+)
+
 // SnapshotInfo contains information about a snapshot.
 // UncompressedSize and NewChunkSize are populated only when the snapshot
 // is present in the local database; LocallyTracked indicates whether
 // those values are meaningful.
+//
+//nolint:tagliatelle // snake_case is the established output format
 type SnapshotInfo struct {
 	ID               types.SnapshotID `json:"id"`
 	Timestamp        time.Time        `json:"timestamp"`
@@ -44,8 +87,8 @@ func formatBytes(bytes int64) string {
 // Format: hostname_snapshotname_2026-01-12T14:41:15Z
 func parseSnapshotTimestamp(snapshotID string) (time.Time, error) {
 	parts := strings.Split(snapshotID, "_")
-	if len(parts) < 2 {
-		return time.Time{}, errors.New("invalid snapshot ID format: expected hostname_snapshotname_timestamp")
+	if len(parts) < minSnapshotIDParts {
+		return time.Time{}, errMalformedSnapshotID
 	}
 
 	// Last part is the RFC3339 timestamp
@@ -65,7 +108,7 @@ func parseSnapshotTimestamp(snapshotID string) (time.Time, error) {
 // Returns the snapshot name, or empty string if the ID is malformed.
 func parseSnapshotName(snapshotID string) string {
 	parts := strings.Split(snapshotID, "_")
-	if len(parts) < 3 {
+	if len(parts) < minSnapshotIDNameParts {
 		// Format: hostname_timestamp — no snapshot name
 		return ""
 	}
@@ -88,7 +131,7 @@ func parseDuration(s string) (time.Duration, error) {
 
 	matches := re.FindAllStringSubmatch(s, -1)
 	if len(matches) == 0 {
-		return 0, fmt.Errorf("invalid duration: %q", s)
+		return 0, fmt.Errorf("%w: %q", errInvalidDuration, s)
 	}
 
 	var total time.Duration
@@ -102,15 +145,15 @@ func parseDuration(s string) (time.Duration, error) {
 		unit := strings.ToLower(match[2])
 		switch unit {
 		case "d", "day", "days":
-			total += time.Duration(n) * 24 * time.Hour
+			total += time.Duration(n) * day
 		case "w", "week", "weeks":
-			total += time.Duration(n) * 7 * 24 * time.Hour
+			total += time.Duration(n) * week
 		case "mo", "month", "months":
-			total += time.Duration(n) * 30 * 24 * time.Hour
+			total += time.Duration(n) * month
 		case "y", "year", "years":
-			total += time.Duration(n) * 365 * 24 * time.Hour
+			total += time.Duration(n) * year
 		default:
-			return 0, fmt.Errorf("unknown time unit %q", unit)
+			return 0, fmt.Errorf("%w %q", errUnknownTimeUnit, unit)
 		}
 	}