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/server/server.go

@@ -148,7 +148,9 @@ func (s *Server) cleanupForExit() {
 func (s *Server) cleanShutdown() {
 	s.exitCode = 0
 
-	ctxShutdown, shutdownCancel := context.WithTimeout(context.Background(), shutdownTimeout)
+	ctxShutdown, shutdownCancel := context.WithTimeout(
+		context.Background(), shutdownTimeout,
+	)
 
 	err := s.httpServer.Shutdown(ctxShutdown)
 	if err != nil {