ci: fix Secret.trim() crash by making TARGET_NODE_PASSWORD a string param

The password() parameter type made params.TARGET_NODE_PASSWORD a
hudson.util.Secret, which has no .trim() method — so the Copy Artifacts
stage crashed with MissingMethodException before doing any work, and all
downstream stages were skipped. A Secret also interpolates to its
encrypted form in "SSHPASS=${...}", which would have broken sshpass auth
even past the crash.

Switch it to a string param so both the validation and the SSHPASS env
interpolation receive plaintext. Note: string params are not masked in
the UI; use a Jenkins credential if masking is required.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: mparamas-zz

Jenkinsfile

@@ -52,10 +52,10 @@ properties([
             defaultValue: '',
             description: '(required when TARGET_NODE_IP is set) SSH username on the flashing host.'
         ),
-        password(
+        string(
             name: 'TARGET_NODE_PASSWORD',
             defaultValue: '',
-            description: '(required when TARGET_NODE_IP is set) SSH password on the flashing host. Passed via the SSHPASS env var, never on the command line.'
+            description: '(required when TARGET_NODE_IP is set) SSH password on the flashing host. Passed via the SSHPASS env var, never on the command line. NOTE: a string param is not masked in the UI; use a Jenkins credential if masking is required.'
         ),
         string(
             name: 'TARGET_DEST_DIR',