Address production-readiness review: clearer errors, safer votes, and ops hardening.

Distinguish auth/lookup failures, make votes idempotent on visible questions, bound shutdown, page admin users, LRU throttle, trusted-proxy CIDRs, avatar cleanup, versioned migrations, and session cleanup logging.

internal/store/sessions.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"errors"
+	"log"
 	"sync"
 	"time"
 
@@ -103,10 +104,21 @@ func (s *SessionStore) cleanupLoop(interval time.Duration) {
 	defer close(s.stopped)
 	ticker := time.NewTicker(interval)
 	defer ticker.Stop()
+	var lastErrLog time.Time
 	for {
 		select {
 		case <-ticker.C:
-			_ = s.q.DeleteExpiredSessions(context.Background())
+			n, err := s.q.DeleteExpiredSessions(context.Background())
+			if err != nil {
+				if time.Since(lastErrLog) > time.Minute {
+					log.Printf("session cleanup: %v", err)
+					lastErrLog = time.Now()
+				}
+				continue
+			}
+			if n > 0 {
+				log.Printf("session cleanup: deleted %d expired row(s)", n)
+			}
 		case <-s.stop:
 			return
 		}