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/broker/broker.go

@@ -21,9 +21,11 @@ func New() *Broker {
 // Wait returns a channel that will be closed when a message is available for the user.
 func (b *Broker) Wait(userID int64) chan struct{} {
 	ch := make(chan struct{}, 1)
+
 	b.mu.Lock()
 	b.listeners[userID] = append(b.listeners[userID], ch)
 	b.mu.Unlock()
+
 	return ch
 }
 
@@ -48,12 +50,15 @@ func (b *Broker) Remove(userID int64, ch chan struct{}) {
 	defer b.mu.Unlock()
 
 	waiters := b.listeners[userID]
+
 	for i, w := range waiters {
 		if w == ch {
 			b.listeners[userID] = append(waiters[:i], waiters[i+1:]...)
+
 			break
 		}
 	}
+
 	if len(b.listeners[userID]) == 0 {
 		delete(b.listeners, userID)
 	}