style: adopt golangci-lint v2 and resolve all findings

Add .golangci.yml (v2): the standard linters plus bodyclose, errorlint, noctx, misspell, rowserrcheck, sqlclosecheck, unconvert, usestdlibvars, with gofumpt + goimports formatters. Enable the std-error-handling exclusion preset for idiomatic Close/Remove/Setenv ignores; scope-exclude SA1019 (parser.ParseDir in tools/openapigen) and ST1005 (intentional capitalized user-facing error copy that tests assert verbatim). No inline nolint directives were introduced.

Resolve all 217 findings behavior-preserving: gofumpt/goimports formatting, explicit blank assignment on intentionally ignored errors, errors.Is/errors.As and %w wrapping, context-aware stdlib calls (CommandContext/QueryContext/NewRequestWithContext/Dialer), staticcheck simplifications, removed redundant conversions, http.StatusOK and http.MethodGet, inlined the go:fix intPtr helper, and deferred sql rows Close. Add a golangci CI job mirroring the existing Go jobs.

.github/workflows/ci.yml

@@ -102,6 +102,21 @@ jobs:
           go test -run '^$' -fuzz 'FuzzParseLink$' -fuzztime=30s ./internal/util/link/
           go test -run '^$' -fuzz 'FuzzDecodeCertPin$' -fuzztime=30s ./internal/web/runtime/
 
+  golangci:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: actions/setup-go@v6
+        with:
+          go-version-file: go.mod
+          cache: true
+      - name: Stub internal/web/dist for go:embed
+        run: mkdir -p internal/web/dist && touch internal/web/dist/.gitkeep
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v8
+        with:
+          version: latest
+
   frontend:
     runs-on: ubuntu-latest
     steps: