fix: install checkout-datetime's missing ui-extensions-react dependency

extensions/checkout-datetime/node_modules had @shopify/ui-extensions but
not @shopify/ui-extensions-react, even though both are declared in its
package.json — npm install was never (re-)run there since the extension's
source was restored (per HANDOVER.md B4). This silently failed every
single `shopify app deploy` for the whole app (esbuild aborts the deploy
when any one extension fails to bundle), which meant the App Proxy URL
fix in shopify.app.toml never actually reached Shopify's servers despite
being correct in the repo — the real cause of the storefront widget's
persistent 500 "Couldn't load available dates" error.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package-lock.json

@@ -63,7 +63,7 @@
         "react": "^18.3.1"
       },
       "devDependencies": {
-        "typescript": "^7.0.2"
+        "typescript": "^5.6.3"
       }
     },
     "extensions/checkout-datetime/node_modules/@shopify/ui-extensions": {
@@ -4060,6 +4060,7 @@
       "cpu": [
         "arm64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4080,6 +4081,7 @@
       "cpu": [
         "arm64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4100,6 +4102,7 @@
       "cpu": [
         "x64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4120,6 +4123,7 @@
       "cpu": [
         "x64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4140,6 +4144,7 @@
       "cpu": [
         "arm"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4160,6 +4165,7 @@
       "cpu": [
         "arm"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4180,6 +4186,7 @@
       "cpu": [
         "arm64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4200,6 +4207,7 @@
       "cpu": [
         "arm64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4220,6 +4228,7 @@
       "cpu": [
         "x64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4240,6 +4249,7 @@
       "cpu": [
         "x64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4260,6 +4270,7 @@
       "cpu": [
         "arm64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [
@@ -4280,6 +4291,7 @@
       "cpu": [
         "x64"
       ],
+      "dev": true,
       "license": "MIT",
       "optional": true,
       "os": [