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.

internal/sub/sub.go

@@ -253,7 +253,7 @@ func (s *Server) Start() (err error) {
 	// This is an anonymous function, no function name
 	defer func() {
 		if err != nil {
-			s.Stop()
+			_ = s.Stop()
 		}
 	}()
 
@@ -288,7 +288,7 @@ func (s *Server) Start() (err error) {
 	}
 
 	listenAddr := net.JoinHostPort(listen, strconv.Itoa(port))
-	listener, err := net.Listen("tcp", listenAddr)
+	listener, err := (&net.ListenConfig{}).Listen(context.Background(), "tcp", listenAddr)
 	if err != nil {
 		return err
 	}
@@ -323,7 +323,7 @@ func (s *Server) Start() (err error) {
 	}
 
 	go func() {
-		s.httpServer.Serve(listener)
+		_ = s.httpServer.Serve(listener)
 	}()
 
 	return nil