Add virtual pages from Shopify and panel refresh button

This simplifies product management by eliminating manual Kirby page creation. Products are now automatically loaded as virtual pages from the Shopify API.

Changes:
- Add virtual pages via page.children:after hook
- Create shopify.php helper with caching (60min TTL)
- Add shopify-refresh panel plugin for cache management
- Remove manual product content files (now virtual)
- Update site.yml blueprint to show refresh button
- Fix cache implementation to use get/set pattern

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

site/plugins/shopify-refresh-button/composer.lock

@@ -0,0 +1,66 @@
+{
+    "_readme": [
+        "This file locks the dependencies of your project to a known state",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
+        "This file is @generated automatically"
+    ],
+    "content-hash": "37a8e61308b9b6f49cb9835f477f0c64",
+    "packages": [
+        {
+            "name": "getkirby/composer-installer",
+            "version": "1.2.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/getkirby/composer-installer.git",
+                "reference": "c98ece30bfba45be7ce457e1102d1b169d922f3d"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/getkirby/composer-installer/zipball/c98ece30bfba45be7ce457e1102d1b169d922f3d",
+                "reference": "c98ece30bfba45be7ce457e1102d1b169d922f3d",
+                "shasum": ""
+            },
+            "require": {
+                "composer-plugin-api": "^1.0 || ^2.0"
+            },
+            "require-dev": {
+                "composer/composer": "^1.8 || ^2.0"
+            },
+            "type": "composer-plugin",
+            "extra": {
+                "class": "Kirby\\ComposerInstaller\\Plugin"
+            },
+            "autoload": {
+                "psr-4": {
+                    "Kirby\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "description": "Kirby's custom Composer installer for the Kirby CMS and for Kirby plugins",
+            "homepage": "https://getkirby.com",
+            "support": {
+                "issues": "https://github.com/getkirby/composer-installer/issues",
+                "source": "https://github.com/getkirby/composer-installer/tree/1.2.1"
+            },
+            "funding": [
+                {
+                    "url": "https://getkirby.com/buy",
+                    "type": "custom"
+                }
+            ],
+            "time": "2020-12-28T12:54:39+00:00"
+        }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": [],
+    "platform-dev": [],
+    "plugin-api-version": "2.6.0"
+}