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>

TODO.md

@@ -14,18 +14,16 @@ pre-1.0
 
 # Next Step
 
-Continue the lint remediation (issue #61): 1,077 findings remain after
-the mechanical chunk. Next chunk candidates: `paralleltest` (137),
-`funcorder` (68), `testpackage` (34), `lll` (79) — still mostly
-mechanical — before the judgment-heavy linters (`revive` 142, `err113`
-96, `mnd` 93, `gosec` 78, `goconst` 55, `cyclop` 52).
+Reconcile the uncommitted ARCHITECTURE.md edits on main: finish and
+commit, or revert.
 
 # Completed Steps
 
-- 2026-08-07: Lint remediation chunk 1 (issue #61): `wsl_v5` (1050),
-  `nlreturn` (378), and `noinlineerr` (373) all fixed to zero via a new
-  `make lint-fix` autofix entrypoint plus hand-fixes; total findings
-  2,990 → 1,077. Full test suite green.
+- 2026-08-07: Updated golangci-lint to v2.12.2 everywhere it is pinned
+  (`Dockerfile` lint stage, `Makefile` deps target), replaced
+  `.golangci.yml` with the canonical config (v2 schema, `default: all`),
+  and remediated all lint findings it surfaced (issue #61):
+  behavior-preserving fixes across every package, `make check` green.
 - 2026-08-07: Added the standard `.golangci.yml` and `.editorconfig`
   (issue #59); lint findings under the new config are tracked in issue
   #61. `script/bootstrap` now installs sqlite3 (needed by tests).
@@ -51,8 +49,6 @@ mechanical — before the judgment-heavy linters (`revive` 142, `err113`
 
 # Future Steps
 
-- Reconcile the uncommitted ARCHITECTURE.md edits on main: finish and
-  commit, or revert.
 - Review stale local branches (add-godoc-to-cli-package,
   feature/pluggable-storage-backend) and merge or delete them.
 - Define remaining scope for a first tagged release and cut v0.1.0.