feat(models): OpenRouter model picker + AJAX refresh + cost preview (v0.11.0 complete)

- AJAX endpoint 'prautoblogger_refresh_models' for manual model registry refresh
- Admin UI button on AI Models tab to trigger refresh (nonce + capability gated)
- Cost preview integration in field renderer using historical token averages
- New public method on Cost Tracker: get_avg_tokens_for_stages(array $stages, int $days = 30): array
- Enhanced field renderer with capability-specific cost calculation (outline+draft+polish for writing, single stage for analysis/editor)
- Autoloader updated to scan ajax/ directory for model registry refresh handler
- Admin JS enhanced with AJAX toggle handler for refresh button
- Template updated with refresh button + nonce in AI Models section
- CHANGELOG + CONVENTIONS + version bump to 0.11.0
- All files under 300-line cap, PHPCS-clean

Spec: https://github.com/peptiderepo/prautoblogger/issues/111
Open questions all resolved per seq-02 plan-ack.

includes/ajax/class-model-registry-refresh.php

@@ -0,0 +1,82 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * AJAX handler to manually refresh the OpenRouter model registry.
+ *
+ * What: Allows admins to trigger an immediate refresh of the cached model
+ *       list via a button in the admin UI, without waiting for the daily
+ *       cron. Useful for testing new models or after adding an API key.
+ * Who calls: Admin-facing JavaScript (model-picker.js) via wp_ajax.
+ * Dependencies: PRAutoBlogger_OpenRouter_Model_Registry, capability gating.
+ *
+ * Triggered by: AJAX POST to 'wp-admin/admin-ajax.php?action=prautoblogger_refresh_models'
+ * Side effects: HTTP GET to OpenRouter /api/v1/models (optional, if 12h window passed);
+ *               wp_options write; transient set.
+ *
+ * @see includes/class-ajax-handlers.php — Instantiation and wiring.
+ * @see assets/js/model-picker.js       — Client-side trigger.
+ * @see services/class-open-router-model-registry.php — Registry that performs the work.
+ */
+class PRAutoBlogger_Model_Registry_Refresh {
+
+	/** @var PRAutoBlogger_OpenRouter_Model_Registry Lazy-loaded singleton. */
+	private PRAutoBlogger_OpenRouter_Model_Registry $registry;
+
+	/**
+	 * @param PRAutoBlogger_OpenRouter_Model_Registry $registry Shared model registry.
+	 */
+	public function __construct( PRAutoBlogger_OpenRouter_Model_Registry $registry ) {
+		$this->registry = $registry;
+	}
+
+	/**
+	 * Handle the AJAX refresh request.
+	 *
+	 * Security: nonce-gated via wp-nonce, capability gated to manage_options.
+	 * Response format: JSON { success: bool, data: { count: int, fetched_at: int, message: string } }
+	 *
+	 * @side-effect Writes HTTP GET request, database options, transient cache.
+	 * @return void (echoes JSON)
+	 */
+	public function handle(): void {
+		// Nonce check.
+		if ( ! isset( $_POST['nonce'] ) || ! wp_verify_nonce( sanitize_text_field( wp_unslash( $_POST['nonce'] ) ), 'prautoblogger_refresh_models' ) ) {
+			wp_send_json_error(
+				[
+					'message' => __( 'Security check failed. Please refresh the page and try again.', 'prautoblogger' ),
+				],
+				403
+			);
+		}
+
+		// Capability check.
+		if ( ! current_user_can( 'manage_options' ) ) {
+			wp_send_json_error(
+				[
+					'message' => __( 'Insufficient permissions. Only administrators can refresh the model list.', 'prautoblogger' ),
+				],
+				403
+			);
+		}
+
+		// Perform the refresh (force=true bypasses the idempotency window).
+		$result = $this->registry->refresh( true );
+
+		$count       = (int) ( $result['count'] ?? 0 );
+		$fetched_at  = (int) ( $result['fetched_at'] ?? 0 );
+		$mins_ago    = $fetched_at > 0 ? intval( ( time() - $fetched_at ) / 60 ) : 0;
+
+		wp_send_json_success(
+			[
+				'count'       => $count,
+				'fetched_at'  => $fetched_at,
+				'message'     => sprintf(
+					__( 'Model registry refreshed: %d models loaded, last updated %s', 'prautoblogger' ),
+					$count,
+					0 === $mins_ago ? __( 'just now', 'prautoblogger' ) : sprintf( __( '%d minutes ago', 'prautoblogger' ), $mins_ago )
+				),
+			]
+		);
+	}
+}