fix: golangci-lint v2 config and lint-clean production code

- Fix .golangci.yml for v2 format (linters-settings -> linters.settings)
- All production code now passes golangci-lint with zero issues
- Line length 88, funlen 80/50, cyclop 15, dupl 100
- Extract shared helpers in db (scanChannels, scanInt64s, scanMessages)
- Split runMigrations into applyMigration/execMigration
- Fix fanOut return signature (remove unused int64)
- Add fanOutSilent helper to avoid dogsled
- Rewrite CLI code for lint compliance (nlreturn, wsl_v5, noctx, etc)
- Rename CLI api package to chatapi to avoid revive var-naming
- Fix all noinlineerr, mnd, perfsprint, funcorder issues
- Fix db tests: extract helpers, add t.Parallel, proper error checks
- Broker tests already clean
- Handler integration tests still have lint issues (next commit)

internal/handlers/handlers.go

@@ -39,7 +39,10 @@ type Handlers struct {
 }
 
 // New creates a new Handlers instance.
-func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
+func New(
+	lc fx.Lifecycle,
+	params Params,
+) (*Handlers, error) {
 	s := new(Handlers)
 	s.params = &params
 	s.log = params.Logger.Get()
@@ -55,12 +58,21 @@ func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
 	return s, nil
 }
 
-func (s *Handlers) respondJSON(w http.ResponseWriter, _ *http.Request, data any, status int) {
-	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+func (s *Handlers) respondJSON(
+	w http.ResponseWriter,
+	_ *http.Request,
+	data any,
+	status int,
+) {
+	w.Header().Set(
+		"Content-Type",
+		"application/json; charset=utf-8",
+	)
 	w.WriteHeader(status)
 
 	if data != nil {
-		if err := json.NewEncoder(w).Encode(data); err != nil {
+		err := json.NewEncoder(w).Encode(data)
+		if err != nil {
 			s.log.Error("json encode error", "error", err)
 		}
 	}