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/sqlc/sessions.sql.go

@@ -10,14 +10,17 @@ import (
 	"time"
 )
 
-const deleteExpiredSessions = `-- name: DeleteExpiredSessions :exec
+const deleteExpiredSessions = `-- name: DeleteExpiredSessions :execrows
 DELETE FROM sessions
 WHERE expiry <= now()
 `
 
-func (q *Queries) DeleteExpiredSessions(ctx context.Context) error {
-	_, err := q.db.ExecContext(ctx, deleteExpiredSessions)
-	return err
+func (q *Queries) DeleteExpiredSessions(ctx context.Context) (int64, error) {
+	result, err := q.db.ExecContext(ctx, deleteExpiredSessions)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected()
 }
 
 const deleteSession = `-- name: DeleteSession :exec