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/snapshot/permission_error_test.go

@@ -1,3 +1,4 @@
+//nolint:testpackage // needs access to unexported wrapPermissionError
 package snapshot
 
 import (
@@ -9,12 +10,15 @@ import (
 	"testing"
 )
 
-func TestWrapPermissionError(t *testing.T) {
-	// Non-permission errors pass through unchanged.
-	plain := errors.New("disk on fire")
+// errDiskOnFire is a non-permission sentinel used to verify pass-through.
+var errDiskOnFire = errors.New("disk on fire")
 
-	got := wrapPermissionError("/some/path", plain)
-	if !errors.Is(got, plain) {
+func TestWrapPermissionError(t *testing.T) {
+	t.Parallel()
+
+	// Non-permission errors pass through unchanged.
+	got := wrapPermissionError("/some/path", errDiskOnFire)
+	if !errors.Is(got, errDiskOnFire) {
 		t.Errorf("non-permission error should pass through, got %v", got)
 	}
 
@@ -32,15 +36,16 @@ func TestWrapPermissionError(t *testing.T) {
 
 	if runtime.GOOS == "darwin" {
 		if !strings.Contains(wrapped.Error(), "Full Disk Access") {
-			t.Errorf("macOS permission error should mention Full Disk Access:\n%s", wrapped.Error())
+			t.Errorf("macOS permission error should mention Full Disk Access:\n%s",
+				wrapped.Error())
 		}
 
 		if !strings.Contains(wrapped.Error(), "System Settings") {
-			t.Errorf("macOS permission error should point at System Settings:\n%s", wrapped.Error())
-		}
-	} else {
-		if !strings.Contains(wrapped.Error(), "--skip-errors") {
-			t.Errorf("non-macOS permission error should mention --skip-errors:\n%s", wrapped.Error())
+			t.Errorf("macOS permission error should point at System Settings:\n%s",
+				wrapped.Error())
 		}
+	} else if !strings.Contains(wrapped.Error(), "--skip-errors") {
+		t.Errorf("non-macOS permission error should mention --skip-errors:\n%s",
+			wrapped.Error())
 	}
 }