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/blob_fetch.go

@@ -14,6 +14,10 @@ import (
 	"sneak.berlin/go/vaultik/internal/log"
 )
 
+// errBlobHashMismatch is returned when a fetched blob's content hash does
+// not match the expected double-SHA-256 hash.
+var errBlobHashMismatch = errors.New("blob hash mismatch")
+
 // hashVerifyReader wraps a blobgen.Reader and verifies the double-SHA-256 hash
 // of decrypted plaintext when Close is called. It reuses the hash that
 // blobgen.Reader already computes internally via its TeeReader, avoiding
@@ -46,7 +50,8 @@ func (h *hashVerifyReader) Close() error {
 
 		actualHashHex := hex.EncodeToString(secondHasher.Sum(nil))
 		if actualHashHex != h.blobHash {
-			return fmt.Errorf("blob hash mismatch: expected %s, got %s", h.blobHash[:16], actualHashHex[:16])
+			return fmt.Errorf("%w: expected %s, got %s",
+				errBlobHashMismatch, h.blobHash[:16], actualHashHex[:16])
 		}
 	}
 
@@ -61,7 +66,9 @@ func (h *hashVerifyReader) Close() error {
 // returns a streaming reader that computes the double-SHA-256 hash on the fly.
 // The hash is verified when the returned reader is closed (after fully reading).
 // This avoids buffering the entire blob in memory.
-func (v *Vaultik) FetchAndDecryptBlob(ctx context.Context, blobHash string, expectedSize int64, identity age.Identity) (io.ReadCloser, error) {
+func (v *Vaultik) FetchAndDecryptBlob(
+	ctx context.Context, blobHash string, expectedSize int64, identity age.Identity,
+) (io.ReadCloser, error) {
 	rc, _, err := v.FetchBlob(ctx, blobHash, expectedSize)
 	if err != nil {
 		return nil, err
@@ -85,7 +92,9 @@ func (v *Vaultik) FetchAndDecryptBlob(ctx context.Context, blobHash string, expe
 // Times the Storage.Get and Storage.Stat round-trips separately at
 // debug level so we can see whether the size-only Stat (which is an
 // extra request on every fetch) is hurting throughput.
-func (v *Vaultik) FetchBlob(ctx context.Context, blobHash string, expectedSize int64) (io.ReadCloser, int64, error) {
+func (v *Vaultik) FetchBlob(
+	ctx context.Context, blobHash string, expectedSize int64,
+) (io.ReadCloser, int64, error) {
 	blobPath := fmt.Sprintf("blobs/%s/%s/%s", blobHash[:2], blobHash[2:4], blobHash)
 
 	t0 := time.Now()