R-899: a daytime press never cancels the night's whole-guest backup (operator ruling 2026-10-08, option A); press sends trigger=manual

Unreleased; ships with tomorrow's release.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/agentapi/client.go

@@ -272,15 +272,7 @@ func (c *Client) BackupDue(ctx context.Context) (DueResponse, error) {
 
 // StartBackup enqueues a backup of this guest (the agent vzdump) and returns the job to poll.
 func (c *Client) StartBackup(ctx context.Context) (BackupResponse, error) {
-	var out BackupResponse
-	body, err := c.post(ctx, "/backup", struct{}{})
-	if err != nil {
-		return out, err
-	}
-	if err := json.Unmarshal(body, &out); err != nil {
-		return out, fmt.Errorf("agentapi: decode POST /backup: %w", err)
-	}
-	return out, nil
+	return c.StartBackupForTrigger(ctx, "", false)
 }
 
 // BackupStatus reports the current/last backup job phase for this guest.