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/vaultik.go

@@ -1,3 +1,5 @@
+// Package vaultik implements the core backup, restore, verify, prune,
+// and snapshot-management operations behind the vaultik CLI.
 package vaultik
 
 import (
@@ -19,6 +21,12 @@ import (
 	"sneak.berlin/go/vaultik/internal/ui"
 )
 
+// Sentinel errors for misconfigured encryption settings.
+var (
+	errNoAgeRecipients = errors.New("no age recipients configured")
+	errNoAgeSecretKey  = errors.New("no age secret key configured")
+)
+
 // Vaultik contains all dependencies needed for vaultik operations
 type Vaultik struct {
 	Globals         *globals.Globals
@@ -32,7 +40,7 @@ type Vaultik struct {
 	Fs              afero.Fs
 
 	// Context management
-	ctx    context.Context
+	ctx    context.Context //nolint:containedctx // ctx bound at construction by design
 	cancel context.CancelFunc
 
 	// IO
@@ -54,8 +62,8 @@ type Vaultik struct {
 	restoreCacheObserver func(*blobDiskCache)
 }
 
-// VaultikParams contains all parameters for New that can be provided by fx
-type VaultikParams struct {
+// Params contains all parameters for New that can be provided by fx
+type Params struct {
 	fx.In
 
 	Globals         *globals.Globals
@@ -71,7 +79,7 @@ type VaultikParams struct {
 
 // New creates a new Vaultik instance with proper context management
 // It automatically includes crypto capabilities if age_secret_key is configured
-func New(params VaultikParams) *Vaultik {
+func New(params Params) *Vaultik {
 	ctx, cancel := context.WithCancel(context.Background())
 
 	// Use provided filesystem or default to OS filesystem
@@ -126,7 +134,7 @@ func (v *Vaultik) CanDecrypt() bool {
 // Returns an error if no recipients are configured
 func (v *Vaultik) GetEncryptor() (*crypto.Encryptor, error) {
 	if len(v.Config.AgeRecipients) == 0 {
-		return nil, errors.New("no age recipients configured")
+		return nil, errNoAgeRecipients
 	}
 
 	return crypto.NewEncryptor(v.Config.AgeRecipients)
@@ -136,19 +144,21 @@ func (v *Vaultik) GetEncryptor() (*crypto.Encryptor, error) {
 // Returns an error if no secret key is configured
 func (v *Vaultik) GetDecryptor() (*crypto.Decryptor, error) {
 	if v.Config.AgeSecretKey == "" {
-		return nil, errors.New("no age secret key configured")
+		return nil, errNoAgeSecretKey
 	}
 
 	return crypto.NewDecryptor(v.Config.AgeSecretKey)
 }
 
 // GetFilesystem returns the filesystem instance used by Vaultik
+//
+//nolint:ireturn // afero.Fs is the filesystem abstraction by design
 func (v *Vaultik) GetFilesystem() afero.Fs {
 	return v.Fs
 }
 
-// printfStdout writes formatted output to stdout.
-func (v *Vaultik) printfStdout(format string, args ...any) {
+// stdoutf writes formatted output to stdout.
+func (v *Vaultik) stdoutf(format string, args ...any) {
 	_, _ = fmt.Fprintf(v.Stdout, format, args...)
 }