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/restore_sweeper.go

@@ -28,7 +28,7 @@ import (
 // which is local, indexed, and not under contention — the queries are
 // cheap and run at most once per blob per sweep interval.
 type restoreSweeper struct {
-	ctx        context.Context
+	ctx        context.Context //nolint:containedctx // ctx bound at construction by design
 	repos      *database.Repositories
 	cache      *blobDiskCache
 	threshold  int64
@@ -38,7 +38,12 @@ type restoreSweeper struct {
 
 // newRestoreSweeper returns a sweeper that triggers eviction every
 // `threshold` bytes restored. Callers should pass blob_size_limit/100.
-func newRestoreSweeper(ctx context.Context, repos *database.Repositories, cache *blobDiskCache, threshold int64) *restoreSweeper {
+func newRestoreSweeper(
+	ctx context.Context,
+	repos *database.Repositories,
+	cache *blobDiskCache,
+	threshold int64,
+) *restoreSweeper {
 	if threshold <= 0 {
 		threshold = 1
 	}
@@ -78,7 +83,8 @@ func (s *restoreSweeper) sweep() {
 	for _, blobHash := range s.cache.Keys() {
 		needed, err := s.blobStillNeeded(blobHash)
 		if err != nil {
-			log.Debug("sweeper referencing-files query failed", "blob_hash", blobHash[:16], "error", err)
+			log.Debug("sweeper referencing-files query failed",
+				"blob_hash", blobHash[:16], "error", err)
 
 			continue
 		}