fix: write SecureNote (camelCase secureNote sub-object per Vaultwarden API)

Vaultwarden post_ciphers expects type=2 data in 'secureNote' field
(camelCase serde), not 'notes'/'secure_note'. Verified end-to-end:
SecureNote create + read works; Login write unchanged.

internal/vaultwarden/api_client.go

@@ -837,7 +837,13 @@ func (ac *APIClient) CreateCipher(in CipherInput) (string, error) {
 			cipher["fields"] = fields
 		}
 	} else if in.Type == CipherTypeSecureNote {
-		// notes already set
+		// Vaultwarden expects type=2 data in the `secureNote` sub-object (camelCase serde).
+		if in.Notes != "" {
+			encNotes, e := EncryptStr(in.Notes, key)
+			if e == nil {
+				cipher["secureNote"] = map[string]interface{}{"notes": encNotes}
+			}
+		}
 	} else {
 		return "", fmt.Errorf("cipher type %d write not supported yet", in.Type)
 	}
@@ -853,6 +859,10 @@ func (ac *APIClient) CreateCipher(in CipherInput) (string, error) {
 	}
 	req.Header.Set("Authorization", "Bearer "+token)
 	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Bitwarden-Client-Version", "2024.1.0")
+	req.Header.Set("User-Agent", "Bitwarden/v2024.1.0")
+	req.Header.Set("Device-Type", "8")
+	req.Header.Set("Accept", "application/json")
 
 	resp, err := ac.httpClient.Do(req)
 	if err != nil {