feat: interactive model picker with searchable popup and pricing

Replace plain text inputs for analysis/writing/editor model fields
with a rich model picker that fetches the OpenRouter model registry
and displays a searchable popup with model name, provider, input/output
pricing per 1M tokens, and context window. Also extracts source status
and model field renderers into dedicated field classes to keep
class-admin-page.php under the 300-line cap.

New files:
- assets/js/model-picker.js — popup UI with search, filtering, caching
- assets/css/model-picker.css — popup styles matching admin design system
- includes/admin/fields/class-open-router-model-field.php — server render
- includes/admin/fields/class-source-status-field.php — extracted field

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

includes/admin/fields/class-source-status-field.php

@@ -0,0 +1,66 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Renders the Reddit source status indicator in the admin settings.
+ *
+ * What: shows RSS (primary) and .json (fallback) availability with
+ *       last-collection timestamp.
+ * Who calls it: PRAutoBlogger_Admin_Page::render_field() delegates here
+ *               for fields with type 'source_status'.
+ * Dependencies: None — reads wp_options only.
+ *
+ * @see admin/class-admin-page.php — Calls render() from the main field switch.
+ */
+class PRAutoBlogger_Source_Status_Field {
+
+	/**
+	 * Render the Reddit source status indicator.
+	 *
+	 * Side effects: reads wp_options for last collection time.
+	 */
+	public static function render(): void {
+		$last_collection  = get_option( 'prautoblogger_last_collection_time', '' );
+		$last_source_used = get_option( 'prautoblogger_last_source_used', '' );
+
+		echo '<div class="ab-source-status">';
+
+		// Reddit RSS — primary source.
+		printf(
+			'<div class="ab-source-row">'
+			. '<span class="ab-source-dot ab-status-ok"></span>'
+			. '<strong>%s</strong> <span class="ab-source-badge">%s</span>'
+			. '<span class="ab-source-label">%s</span>'
+			. '</div>',
+			esc_html__( 'Reddit RSS', 'prautoblogger' ),
+			esc_html__( 'Primary', 'prautoblogger' ),
+			esc_html__( 'Reliable from all IPs', 'prautoblogger' )
+		);
+
+		// Reddit .json — fallback source.
+		printf(
+			'<div class="ab-source-row">'
+			. '<span class="ab-source-dot ab-status-ok"></span>'
+			. '<strong>%s</strong> <span class="ab-source-badge ab-badge-secondary">%s</span>'
+			. '<span class="ab-source-label">%s</span>'
+			. '</div>',
+			esc_html__( 'Reddit .json', 'prautoblogger' ),
+			esc_html__( 'Fallback + Comments', 'prautoblogger' ),
+			esc_html__( 'May be IP-blocked on some hosts', 'prautoblogger' )
+		);
+
+		// Last collection info.
+		if ( '' !== $last_collection ) {
+			$time_ago = human_time_diff( (int) $last_collection, time() );
+			printf(
+				'<div class="ab-source-meta">%s <strong>%s</strong> %s</div>',
+				esc_html__( 'Last collection:', 'prautoblogger' ),
+				/* translators: %s is a human-readable time difference like "2 hours" */
+				esc_html( sprintf( __( '%s ago', 'prautoblogger' ), $time_ago ) ),
+				'' !== $last_source_used ? esc_html( sprintf( __( 'via %s', 'prautoblogger' ), $last_source_used ) ) : ''
+			);
+		}
+
+		echo '</div>';
+	}
+}