feat: Pipeline Settings M1 — per-step model picker, system instructions, agent prompts (#170, v0.23.0)

Additive per-step Pipeline Settings page. Reuses the existing model_select picker + versioned prompt registry; no migration. QA APPROVE for eea4968; CI green.

Agent-Session: pipeline-settings-m1-merge

assets/js/pipeline-settings.js

@@ -0,0 +1,24 @@
+/**
+ * Pipeline Settings page — step rail and prompt editor interactions.
+ *
+ * Responsibilities:
+ *   - Confirm before resetting a prompt to default (redundant safety; the
+ *     PHP onclick already handles it, but JS enhances UX).
+ *
+ * Note: model selection is handled entirely by model-picker.js, which writes
+ * the chosen model id directly to the hidden input named after the option
+ * (e.g. name="prautoblogger_research_model"). No event bridge is needed here —
+ * the form submits that value on the standard POST to handle_model_save().
+ *
+ * @see admin/class-pipeline-settings-save-handler.php — Reads $_POST[$option_name].
+ * @see assets/js/model-picker.js              — Writes to the hidden input by DOM id.
+ */
+/* global jQuery */
+( function ( $ ) {
+	'use strict';
+
+	$( function () {
+		// Future UX hooks (e.g. unsaved-changes warning) go here.
+	} );
+
+}( jQuery ) );