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

Adds a new 'Pipeline' wp-admin submenu page (prautoblogger-pipeline) with a
step rail covering all LLM stages: Research, Analysis, Writer, Editorial, Image.

Per-step panels surface:
- The existing PRAutoBlogger_OpenRouter_Model_Field picker (no new dropdown) with
  stage-accurate cost-preview for each step.
- System-instructions editor + agent-prompt editor(s) bound to the versioned
  prompt registry. Saving creates a new immutable version; reset-to-default
  available; active version number shown per panel.
- Step params read from PRAutoBlogger_Prompt_Registry::defs() (read-only in M1).

Writer panel marks inactive sub-stage prompts based on current pipeline mode.

No existing Settings sections changed — both surfaces edit the same wp_options
and prompts table. Decomposition of AI Models / Content / Sources tabs is M2.

get_stages_for_setting() extended: prautoblogger_research_model → [research,
llm_research] and prautoblogger_image_model → [image_a, image_b] for
cost-preview accuracy.

New files (4 classes + 1 CSS + 1 JS + 2 templates, all <=300 lines):
  includes/admin/class-pipeline-settings-page.php
  includes/admin/class-pipeline-settings-renderer.php
  includes/admin/class-pipeline-settings-save-handler.php
  includes/admin/class-pipeline-settings-step-map.php
  assets/css/pipeline-settings.css
  assets/js/pipeline-settings.js
  templates/admin/pipeline-settings-page.php
  templates/admin/pipeline-settings-prompt-panel.php

Modified:
  includes/admin/fields/class-open-router-model-field.php
  includes/class-prautoblogger.php
  prautoblogger.php (v0.23.0)
  ARCHITECTURE.md / INFORMATION-ARCHITECTURE.md / CHANGELOG.md

No new wp_options; uninstall unchanged.

Agent-Session: pipeline-settings-m1

assets/js/pipeline-settings.js

@@ -0,0 +1,34 @@
+/**
+ * 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).
+ *   - Wire the model-picker hidden input so the save_model form picks up
+ *     the newly selected model id from the popup.
+ *
+ * @see admin/class-pipeline-settings-page.php — Enqueues this script.
+ * @see assets/js/model-picker.js              — Handles the picker popup.
+ */
+/* global jQuery */
+( function ( $ ) {
+	'use strict';
+
+	$( function () {
+
+		// When the model picker JS selects a model, update the hidden
+		// 'model_id' input in the same .pab-model-form so the save form
+		// carries the chosen value on submit.
+		$( document ).on( 'prautoblogger:model_selected', function ( e, data ) {
+			var $form = $( '.pab-model-form' );
+			var $hidden = $form.find( 'input[name="model_id"]' );
+			if ( 0 === $hidden.length ) {
+				$hidden = $( '<input type="hidden" name="model_id" />' );
+				$form.append( $hidden );
+			}
+			$hidden.val( data.model_id || data.id || '' );
+		} );
+
+	} );
+
+}( jQuery ) );