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/pidlock/pidlock.go

@@ -21,6 +21,13 @@ type Lock struct {
 	path string
 }
 
+const (
+	// lockDirPerm is the mode for the lock directory (owner-only).
+	lockDirPerm = 0o700
+	// pidFilePerm is the mode for the PID file (owner-only).
+	pidFilePerm = 0o600
+)
+
 // Acquire attempts to acquire a PID lock in the specified directory.
 // If the lock file exists and the process is still running, it returns
 // ErrAlreadyRunning with details about the existing process.
@@ -28,7 +35,8 @@ type Lock struct {
 // a Lock that must be released with Release().
 func Acquire(lockDir string) (*Lock, error) {
 	// Ensure lock directory exists
-	if err := os.MkdirAll(lockDir, 0700); err != nil {
+	err := os.MkdirAll(lockDir, lockDirPerm)
+	if err != nil {
 		return nil, fmt.Errorf("creating lock directory: %w", err)
 	}
 
@@ -46,7 +54,9 @@ func Acquire(lockDir string) (*Lock, error) {
 
 	// Write our PID
 	pid := os.Getpid()
-	if err := os.WriteFile(lockPath, []byte(strconv.Itoa(pid)), 0600); err != nil {
+
+	err = os.WriteFile(lockPath, []byte(strconv.Itoa(pid)), pidFilePerm)
+	if err != nil {
 		return nil, fmt.Errorf("writing PID file: %w", err)
 	}
 
@@ -64,7 +74,7 @@ func (l *Lock) Release() error {
 	existingPID, err := readPIDFile(l.path)
 	if err != nil {
 		// File already gone or unreadable - that's fine
-		return nil
+		return nil //nolint:nilerr // unreadable lock file means nothing to release
 	}
 
 	if existingPID != os.Getpid() {
@@ -84,7 +94,7 @@ func (l *Lock) Release() error {
 
 // readPIDFile reads and parses the PID from a lock file.
 func readPIDFile(path string) (int, error) {
-	data, err := os.ReadFile(path)
+	data, err := os.ReadFile(path) //nolint:gosec // G304: path is our own lock file
 	if err != nil {
 		return 0, err
 	}