Update golangci-lint to v2.12.2 with canonical config (#29)

Bumps golangci-lint from v2.1.6 (digest-only pin in the `Dockerfile` lint stage) to v2.12.2, pinned by tag and digest (Debian-based image).

Replaces `.golangci.yml` with the canonical strict config: all linters enabled except the standard disable list (`exhaustruct`, `depguard`, `godot`, `wsl`, `wrapcheck`, `varnamelen`), `lll` at 88, `funlen` 80/50, `cyclop` 15, `dupl` 100, and test files are now linted (the old config had `tests: false`, an enable-only list of ~20 linters, `lll` 120, and a blanket exclusion of `internal/macse`).

The stricter config surfaced ~1550 findings, all fixed:

- `wsl_v5` (439) / `nlreturn` (24): blank-line insertions
- `lll` (309): line wrapping at 88 columns; long literals split with `+` concatenation, values unchanged
- `noinlineerr` (130): `if err := ...` split into assignment plus check
- `paralleltest` (116): `t.Parallel()` added to tests without shared state; reasoned `//nolint` where `t.Setenv` or shared fixtures forbid it
- `err113` (97): package-level sentinel errors (new `internal/vault/errors.go`), `%w` wrapping, `errors.Is`
- `perfsprint` (74) / `modernize` (39) / `intrange`: `strconv`, `errors.New`, `slices.Contains`, `any`, `SplitSeq`
- `goconst` (40) / `dupword` (41) / `testifylint` (42) / `thelper` (33): constants, assertion fixes, `t.Helper()`
- `noctx` (22): `exec.CommandContext` for gpg/CLI invocations
- `testpackage` (18): black-box tests moved to `_test` packages where they use only exported identifiers; white-box files carry a reasoned `//nolint`
- `funlen`/`cyclop`/`gocognit`/`nestif`/`dupl`: behavior-preserving helper extraction
- assorted singletons: `gosec`, `gosmopolitan`, `funcorder`, `nonamedreturns`, `makezero`, `prealloc`, `godox`, `nolintlint`, `ireturn`, `nilnil`, `gochecknoinits`

## User-visible strings

**None changed.** Every error message this branch composes is byte-identical to the one `main` composes.

The `err113` sentinels are shaped so `fmt.Errorf` reassembles the original text around them: the sentinel carries the fixed words and the caller supplies the interpolated value in the position it has always occupied. Where the value sits mid-sentence the sentinel holds only a fragment (e.g. `vault.ErrVaultNotFound` is `"does not exist"`, composed by its caller as `vault <name> does not exist`); each such sentinel documents the message it participates in.

Verified mechanically, not by inspection: every `fmt.Errorf` and `errors.New` call site in both trees is parsed, the `Error()` text of any sentinel passed to `%w` is substituted in, and the resulting sets of composed message templates are compared. All 350 templates `main` produces are still produced, character for character. The set of lost or altered messages is empty.

## `unlocker list`

`findUnlockerIDByMetadata` returns `(string, error)` rather than signalling failure with an empty ID, so an unreadable `unlockers.d` is no longer indistinguishable from "no matching entry". `UnlockersList` skips such an entry with a warning naming the directory — its behavior before the scan was extracted into a helper — instead of emitting a row under a synthesized fallback ID that no `unlocker remove` or `unlocker select` can match and that suppresses the current-unlocker marker. The duplicate-check and shell-completion callers skip on the same condition, matching their pre-extraction behavior. Covered by `internal/cli/unlockers_list_test.go`.

`TODO.md` records the change plus follow-ups (version-completion TODOs formerly in code comments, darwin-gated files exceeding 88 columns that Linux CI does not lint).

`make check` is green and the pinned v2.12.2 image reports `0 issues.` Note the test suite needs the memlock ulimit from `script/cibuild` for the 10MB memguard test; that requirement is pre-existing.

Not changed: `script/bootstrap` installs golangci-lint via the system package manager (no version pin to bump), and `script/lint` invokes whatever `golangci-lint` is on PATH. golangci-lint v2.12 deprecates `gomodguard` in favor of `gomodguard_v2` (warning only); the canonical config owns that decision.

Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #29
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/secret/seunlocker_stub.go

@@ -1,22 +1,25 @@
 //go:build !darwin
-// +build !darwin
 
 package secret
 
 import (
-	"fmt"
+	"errors"
 
 	"filippo.io/age"
 	"github.com/spf13/afero"
 )
 
-var errSENotSupported = fmt.Errorf(
+// seUnlockerType is the type string for Secure Enclave unlockers.
+const seUnlockerType = "secure-enclave"
+
+var errSENotSupported = errors.New(
 	"secure enclave unlockers are only supported on macOS",
 )
 
 // SecureEnclaveUnlockerMetadata is a stub for non-Darwin platforms.
 type SecureEnclaveUnlockerMetadata struct {
 	UnlockerMetadata
+
 	SEKeyLabel string `json:"seKeyLabel"`
 	SEKeyHash  string `json:"seKeyHash"`
 }
@@ -28,6 +31,21 @@ type SecureEnclaveUnlocker struct {
 	fs        afero.Fs
 }
 
+// NewSecureEnclaveUnlocker creates a stub SecureEnclaveUnlocker on
+// non-Darwin platforms. The returned instance's methods that require
+// macOS functionality will return errors.
+func NewSecureEnclaveUnlocker(
+	fs afero.Fs,
+	directory string,
+	metadata UnlockerMetadata,
+) *SecureEnclaveUnlocker {
+	return &SecureEnclaveUnlocker{
+		Directory: directory,
+		Metadata:  metadata,
+		fs:        fs,
+	}
+}
+
 // GetIdentity returns an error on non-Darwin platforms.
 func (s *SecureEnclaveUnlocker) GetIdentity() (*age.X25519Identity, error) {
 	return nil, errSENotSupported
@@ -35,7 +53,7 @@ func (s *SecureEnclaveUnlocker) GetIdentity() (*age.X25519Identity, error) {
 
 // GetType returns the unlocker type.
 func (s *SecureEnclaveUnlocker) GetType() string {
-	return "secure-enclave"
+	return seUnlockerType
 }
 
 // GetMetadata returns the unlocker metadata.
@@ -50,10 +68,7 @@ func (s *SecureEnclaveUnlocker) GetDirectory() string {
 
 // GetID returns the unlocker ID.
 func (s *SecureEnclaveUnlocker) GetID() string {
-	return fmt.Sprintf(
-		"%s-secure-enclave",
-		s.Metadata.CreatedAt.Format("2006-01-02.15.04"),
-	)
+	return s.Metadata.CreatedAt.Format("2006-01-02.15.04") + "-" + seUnlockerType
 }
 
 // Remove returns an error on non-Darwin platforms.
@@ -61,20 +76,6 @@ func (s *SecureEnclaveUnlocker) Remove() error {
 	return errSENotSupported
 }
 
-// NewSecureEnclaveUnlocker creates a stub SecureEnclaveUnlocker on non-Darwin platforms.
-// The returned instance's methods that require macOS functionality will return errors.
-func NewSecureEnclaveUnlocker(
-	fs afero.Fs,
-	directory string,
-	metadata UnlockerMetadata,
-) *SecureEnclaveUnlocker {
-	return &SecureEnclaveUnlocker{
-		Directory: directory,
-		Metadata:  metadata,
-		fs:        fs,
-	}
-}
-
 // CreateSecureEnclaveUnlocker returns an error on non-Darwin platforms.
 func CreateSecureEnclaveUnlocker(
 	_ afero.Fs,