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/web/job/check_memory_usage.go

@@ -2,15 +2,12 @@ package job
 
 import (
 	"github.com/mhsanaei/3x-ui/v3/internal/eventbus"
-	"github.com/mhsanaei/3x-ui/v3/internal/web/service"
 
 	"github.com/shirou/gopsutil/v4/mem"
 )
 
 // CheckMemJob monitors memory usage and publishes events when threshold is exceeded.
-type CheckMemJob struct {
-	settingService service.SettingService
-}
+type CheckMemJob struct{}
 
 // NewCheckMemJob creates a new memory monitoring job instance.
 func NewCheckMemJob() *CheckMemJob {