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.

assets/js/admin.js

@@ -446,4 +446,49 @@
 		});
 	});
 
+
+	// Refresh model registry button.
+	$(document).on('click', '#prautoblogger-refresh-models', function (e) {
+		e.preventDefault();
+		var $btn = $(this);
+		var nonce = $btn.data('nonce');
+		var originalText = $btn.html();
+
+		$btn.prop('disabled', true).addClass('ab-btn-loading');
+
+		$.ajax({
+			url: ajaxurl,
+			method: 'POST',
+			data: {
+				action: 'prautoblogger_refresh_models',
+				nonce: nonce
+			},
+			timeout: 30000
+		})
+		.done(function (response) {
+			if (response.success && response.data && response.data.message) {
+				// Show success toast
+				var $notice = $('<div class="ab-save-notice" role="status"></div>')
+					.html('<span class="dashicons dashicons-yes"></span> ' + response.data.message)
+					.insertBefore('.ab-layout')
+					.delay(4000)
+					.fadeOut(function () {
+						$(this).remove();
+					});
+			}
+		})
+		.fail(function () {
+			var $notice = $('<div class="ab-save-notice notice-error" role="alert"></div>')
+				.html('<span class="dashicons dashicons-warning"></span> ' + 'Failed to refresh model list. Please try again.')
+				.insertBefore('.ab-layout')
+				.delay(5000)
+				.fadeOut(function () {
+					$(this).remove();
+				});
+		})
+		.always(function () {
+			$btn.prop('disabled', false).removeClass('ab-btn-loading').html(originalText);
+		});
+	});
+
 })(jQuery);