feat: Live Runware model catalog sync — v0.15.0

Implements daily WP-Cron sync from Runware's /v1/models endpoint with 24h TTL caching,
on-demand AJAX refresh button in PRAdmin (Images settings), smart fallback logic, and
pricing merge from the authoritative cost table.

## Key additions:
- class-runware-model-catalog.php: ~300 lines, fetches/normalizes/caches models,
  exposes sync()/get_models()/get_last_synced_at()/is_stale() public API
- AJAX handler: prautoblogger_sync_runware_models_now with nonce + manage_options check
- Daily cron registered on activation, unscheduled on deactivation
- Caching strategy: <24h fresh → use cache; stale → sync; sync fails → fallback
- Pricing merge: costs from class-runware-image-pricing.php injected on every sync
- Fallback never returns empty array (hardcoded 15-model list)
- Unit tests: sync success/failure, stale cache, fallback behavior, pricing merge

## File changes:
- class-image-model-registry.php: refactored to delegate Runware to catalog,
  extracted get_runware_fallback_models() and get_openrouter_models()
- class-settings-fields-extended.php: added runware_catalog_sync field type
  for status display + Sync button in Images settings section
- class-prautoblogger.php: registered daily cron + AJAX hook
- class-activator.php: schedule prautoblogger_sync_runware_models on activation
- class-deactivator.php: unschedule on deactivation
- class-ajax-handlers.php: added on_ajax_sync_runware_models_now() handler
- class-runware-image-pricing.php: added @see cross-reference to catalog
- ARCHITECTURE.md: updated Runware row in External API Integrations table
- prautoblogger.php: version bump to 0.15.0
- CHANGELOG.md: detailed entry describing the fix and why it was necessary

Fixes the pattern from v0.13.8 and v0.14.0 where hardcoded Runware model
expansion without pricing class updates led to silent fallback-to-schnell bugs.

includes/class-ajax-handlers.php

@@ -157,6 +157,54 @@ class PRAutoBlogger_Ajax_Handlers {
 	 * @return PRAutoBlogger_OpenRouter_Model_Registry
 	 */
 	public function get_registry(): PRAutoBlogger_OpenRouter_Model_Registry {
+
+	/**
+	 * AJAX handler: sync Runware model catalog on demand.
+	 *
+	 * Nonce-protected and requires manage_options capability.
+	 * Returns the updated cache timestamp and model count.
+	 *
+	 * Side effects: makes HTTP request to Runware API, writes WP options.
+	 */
+	public function on_ajax_sync_runware_models_now(): void {
+		check_ajax_referer( 'prautoblogger_sync_runware_models_now', 'nonce' );
+
+		if ( ! current_user_can( 'manage_options' ) ) {
+			wp_send_json_error( array( 'message' => __( 'Insufficient permissions.', 'prautoblogger' ) ), 403 );
+			return;
+		}
+
+		try {
+			$catalog = new PRAutoBlogger_Runware_Model_Catalog();
+			$success = $catalog->sync();
+
+			if ( ! $success ) {
+				wp_send_json_error( array( 'message' => __( 'Catalog sync failed. Check logs for details.', 'prautoblogger' ) ) );
+				return;
+			}
+
+			$models = $catalog->get_models();
+			$synced_at = $catalog->get_last_synced_at();
+			$synced_at_str = $synced_at
+				? wp_date( __( 'Y-m-d H:i:s', 'prautoblogger' ), $synced_at )
+				: __( 'Never', 'prautoblogger' );
+
+			wp_send_json_success(
+				array(
+					'message'   => __( 'Runware model catalog synced successfully.', 'prautoblogger' ),
+					'model_count' => count( $models ),
+					'synced_at' => $synced_at_str,
+				)
+			);
+		} catch ( \Throwable $e ) {
+			PRAutoBlogger_Logger::instance()->error(
+				sprintf( 'AJAX sync Runware models failed: %s (%s)', $e->getMessage(), get_class( $e ) ),
+				'runware-catalog'
+			);
+			wp_send_json_error( array( 'message' => $e->getMessage() ) );
+		}
+	}
+
 		return $this->model_registry;
 	}
 }